Personality Swap

Taking body swap to a whole new level...

Jackie: Use my chi for the transfusion.

Jade: [gives Jackie an "Uncle smack"] I do not know such spells. Jade has Uncle's chi, not his brain.

—Jackie Chan Adventures, "Chi of the Vampire"

A variation on the traditional Freaky Friday Flip plot, wherein two characters don't swap bodies, but they do swap personalities and temperament. The key difference being that things such as intellect, skills, and abilities don't alter.

As it isn't a mind swap you don't get to play with the Gender Bender or Black Like Me and similar tropes; also unlike in a Freaky Friday Flip the voices (even in animation) don't switch. However, you can draw humor from making one character act like his exact opposite. This can lead to things like 50-year-old men acting like teenage girls, or the usually bookish teacher's pet suddenly becoming a rebel.

The reason for this change can be Green Rocks, Applied Phlebotinum but frequently even some naturally occurring non-fantastic explanation such as Acquired Situational Narcissism, a changing of clothes, habits, jobs or maybe The Mind Is a Plaything of the Body.

Examples of Personality Swap include:

Anime and Manga

One confusing episode of Martian Successor Nadesico centered around several of the characters' minds being linked together by the enemy robots (or something like that). While they were connected, they were unable to consciously control their own bodies, which were then taken over by their suppressed personality traits. It led to Action Girl Ryoko cowering in fear, Ms. Exposition Inez refusing to explain things, and eternal sadsack Jun grabbing a machine gun and running around in search of things to shoot.
Parodied in the Fourth Wall Mail Slot in one volume of Eyeshield 21 - A reader asks what would happen if Hiruma and Mamori switched personalities. They come to the conclusion it's best the way it is.
Axis Powers Hetalia has Germany and Italy try and act like each other in one comic.
Maria Holic has Matsurika use Sleep Learning to change Kanako from a giddy, rambling idiot into someone closer to a Class Representative. To Mariya's surprise, while Kanako's personality is much more stubborn, her perversions haven't changed a bit.
The third episode of Makai Senki Disgaea has Etna and Flonne exchanging everything but their actual identity. This includes their clothes.
This actually is involved with a Freaky Friday Flip in The World God Only Knows. Yui and Keima switch bodies but otherwise act like their normal selves...until later in the arc when they begin assuming the personality of the other person when Keima gets flustered by close physical contact with his own body like Yui did not long before and Yui starts picking up on masculine pronouns and things. Things go back to normal before the situation can degenerate any further, however. The implication is that the runaway spirit over time would have basically modeled them into the bodies they possessed in an attempt to gain its resurrection.
One chapter of Pokémon Special had Red and Green accidentally trading their teams. Because of the contrasting personalities of the trainers, the Pokémon had to adjust: Red teaches Green's Pokémon to be more laid-back and relaxed, while Green trains Red's team into battle-hardened warriors. By the time they switched back at the end of the chapter, neither trainer is amused at the results (Red had to run for his life from his Pokémon, and Green is weirded out by his team having mellowed out). It's also plot-relevant, since the trading sequence allowed Green to evolve his Machoke into Machamp, and a previously recalcitrant Porygon now snuggling up to him.

Film

Young Frankenstein. Done in part and deliberately.

Literature

The 2nd part of the Star Trek audio book Spock VS Q has this befall the titular characters after a casual handshake. Utter hilarity ensues.

Live Action TV

Happens in an episode of Seinfeld to Jerry and Kramer when they switch apartments.
- Also happens in another episode where, by withholding from sex, George becomes smart and successful and Elaine suffers a severe drop in intelligence.
An episode of Sabrina the Teenage Witch has this happen to Zelda and Hilda who willingly purchase some pairs of magical 'Walk in my Moccasins' to get a better perspective on each other.
- Also happened, thanks to sunspots, with Sabrina and Libby. However, they did not act exactly like each other—Libby went from being the Alpha Bitch to a Friend to All Living Things, and Sabrina went from being her normal self to militaristic would be Evil Overlord with plans to Take Over the World (with a little prodding from Salem).
  - Done again during Sabrina's time at Scorch magazine, when she tries to make notoriously unpleasant rapper Baby B 2 K "like her" as in, enjoy her company, and Baby ends up "like her" as in, personality-wise. Baby ends up baking the paparazzi pecan sandies, and Sabrina takes on a jerk neighbor in small claims court.
On News Radio, meek man-child Matthew becomes the office jerk after he asserts himself to Bill (by punching his lights out), who in turn takes Matthew's place as the meek one. The status quo is restored when Bill, trying to defend Matthew, accidentally slaps him in the face, causing Matthew to snap out of his power trip.
In a later episode of Sesame Street, Oscar and Telly get three wishes between them. Telly wishes Oscar would be a nice person, and Oscar wishes Telly would be a grouch... and this briefly happens. Then the person who gave out the wishes reverses those two.
Also on Sesame Street, in episode 720, Ernie imagines switching personalities with Bert.
Space Cases: An "experiment" by Miss Davenport causes the kids to "change identities"; they don't swap bodies but species, along with the accompanying abilities and powers. Since The Mind Is a Plaything of the Body, turning human turns the normally quiet Radu into a take-charge leader (but unable to handle leadership), Bova turns into a Mercurian and becomes "cheery, bright, and sunny," and Rosie turns into a Uranus-ian(?) and becomes the Grumpy Bear.
In the Star Trek: The Next Generation episode "Transfigurations" Dr. Crusher finds that to save a shuttle crash victim she needed someone to volunteer a neural link to help regulate their brain functions. Geordi volunteers and because the individual was undergoing a type of Ascending to a Higher Plane of Existence transformation the leftover impression gave Geordi an amazing boost in confidence especially with romantic pursuits.
- Similarly, in "Sarek" Picard mind-melds with Sarek, giving the aging Vulcan his emotional strength, while receiving the consequences of Sarek's Vulcan Alzheimer's, so that Sarek can complete a diplomatic negotiation.
In Quantum Leap, a freak accident switches Sam and Al's roles, with Al now trapped in time and Sam as a computer projection finding advice and information. The switch also makes Al more virtuous and Sam more lecherous, confounding them both.
On 30 Rock, when Liz gets a job hosting her own talk show, it gives her Acquired Situational Narcissism and she starts acting like a delusional diva... in other words, like Jenna. Meanwhile, Frank is promoted to show runner on TGS and starts acting (and looking!) like Liz.
Happened a few times on Home Improvement. Every so often Tim would shift character positions with someone else as they act more impulsive like Tim would normally. When Wilson was thinking of moving back to where he use to live with his (now deceased) wife because her memory was fading, they actually swapped sides of the fence as Tim gives him advice on how to remember departed loved ones. When Al took on as a guest host for a cooking show and Tim took up as a dedicated assistant, Al ended up being arrogant and refused the practical advice Tim would give.

Video Games

Apparently, one of the plans in Crash Twinsanity, was to make it so that when they go to the Tenth Dimension, Crash and Cortex switch personalities, unfortunately, this was removed from the game.

Western Animation

American Dad: In "Rough Trade", Stan is sentenced to house arrest for driving drunk, and Roger sets out to prove he can be a provider. Roger becomes the family role model, Stan becomes the obnoxious drunk.

Stan: Eeeeh. Preeeetty sure I asked for pecan sandies.

In the Jackie Chan Adventures episode "Chi of the Vampire" a Chinese Vampire absorbed several characters' chi; which mean they needed 'chi transfusions'. This led to Tohru becoming like Jade, and Jade becoming like Uncle, providing the above quote.
What's New, Scooby-Doo?: In "A Terrifying Round with a Menacing Metallic Clown": Due to Velma's coulrophobia and Shaggy's desire to win a mini-golf tournament, meaning nothing is going to stop him, they switch personas (and positions within the Mystery Inc. gang) for an episode when a Monster Clown shows up... mostly.

Daphne: How about you, Velma? Would you do it for a Scooby Snack?
Velma: Please, I'm scared. Not desperate.

One episode of The Simpsons has Bart and Lisa swap social positions (if not total personalities) after a Inept Aptitude Test. Bart becomes the good student when he finds that his career path is in law enforcement and is given the Hall Monitor position. Lisa, finding her path to be as just a homemaker, starts acting out and hanging with the bad girls. Their personalities don't exactly switch, however: Bart basically becomes a justified thug while Lisa uses her intelligence to best effect when rebelling against everybody. The Status Quo gets restored when Bart takes the fall for Lisa's theft of the teachers' guides because even he recognizes that she has a better future than he does.
- A similar thing happened in another episode where the Simpsons got a pool and Bart ended up breaking his leg and had to be cooped up in the house all summer. Lisa became wildly popular with the other kids while Bart became bitter and reclusive. However, Lisa's popularity fades when Martin gets an even better pool, and the Status Quo is restored.
Also happened on Daria once. After Quinn became reclusive and antisocial, Daria intentionally became fashionable and flighty to bring Quinn out of it. Episode title being Quinn the Brain.
Done in the Totally Spies! episode "Totally Switched". Clover's personality is swapped with Jerry's by use of a crazy psychologist's behavioral adjusting amulet.

Clover: Oh... good heavens.
Jerry: No freakin' way!!
Sam: O.. kay, this is the weirdest moment ever.

In one episode of Harvey Birdman, Attorney at Law, X the Eliminator gets Birdman's crest and becomes successful and well-liked, while Birdman becomes an obsessive stalker (building a death ray console).
My Little Pony: In "Mish Mash Melee," Gusty, Fizzy, Shady, and Wind Whistler stumble across the Applied Phlebotinum that maintains "the balance of nature," and their personalities become the opposite of their true nature.
Dragon Tales did this to Zak and Wheezie in one episode via a magic statue. As they share the same body, the Freaky Friday plot wouldn't be an option anyway.
In the Kim Possible episode "Bad Boy", Applied Phlebotinum causes Sidekick Ron to gradually become evil while Mad Scientist Drakken turns good.
- In the Post Script Season episode "Stop Team Go", the same Applied Phlebotinum is now turned into a Mirror Morality Machine and causes instant alignment switches. Team Go becomes evil and Shego turns good to become Kim's best friend; The KiGo shippers Squee as their dreams almost become Canon.
Inhumanoids had Magnokor and Metlar switch alignment after the former boosted their magnetic powers through a boulder of galvacite to finally defeat their arch-enemy.
The episode of The Ren and Stimpy Show entitled "Who's Stupid Now?" had Ren forced to be "the fat, stupid one" and Stimpy "the skinny jerk" thanks to in-episode Executive Meddling. Stimpy later gains intelligence on his own and becomes more abusive towards Ren.
This happens in an episode of SpongeBob SquarePants where Squidward gets electrocuted by his electric fence and gets a personality similar to SpongeBob's, and then at the end of the episode where SpongeBob gets electrified by the same fence and ends up with a personality like Squidward's.
Even Winnie the Pooh has done this—more specifically, Happy Pooh Year (released together with Winnie the Pooh and Christmas Too as A Very Merry Pooh Year), with the switch done in two pairs: Tigger and Piglet, and Pooh and Eeyore. Frankly, seeing the usually gloomy Eeyore acting like Pooh and grinning like a madman is... disturbing.
- Additionally, The New Adventures Of Winnie The Pooh's episode "Sham Pooh" features Pooh losing his appetite, causing the gang to suspect that he's not, in fact, Pooh. It is then determined that Owl is actually Pooh, Gopher is Owl, Piglet is Gopher, and Rabbit is Piglet. (Only Tigger remains himself, and he's also the one who's having the most fun watching everything unfold.) The characters act accordingly up until Pooh starts eating honey again.
In an episode of The Lion King spinoff "Timon and Pumbaa", the titular pair think they're going to die as a result of eating poison bugs. During their "last days", the pair undergo a personality swap-the usually selfish and greedy Timon gives away all his earthly posessions and finds joy in kindness and generosity, while the formerly kind-hearted Pumbaa becomes self-centered and vain, wanting to live it up before he goes out. Naturally, when it is revealed that death isn't imminent, the pair revert to their usual personalities.
The Ed, Edd 'n' Eddy episode "Mirror, Mirror on the Ed" has the Eds daring each other to act like another Ed. Ed imitates Eddy ("I'll do anything for cash, 'cause I'm short."), Edd imitates Ed ("Gravy!"), and Eddy imitates Edd ("Oh, the insanitary! My skinny arms cannot bear the weight.")
Time Squad does this without a plot device at all- after a fierce argument, the fussy, cultured Larry and overly manly Buck cordon off the space station to avoid each other, only to realise that everything they like is on the other one's side of the station. So out of boredom, Buck starts learning gourmet cooking, while Larry is irresponsible with a BFG.
Phineas and Ferb played with this in one episode. Everyone's roles and Catch Phrases were shuffled around. Doofinshmirtz built a giant city (with Norm as the guy who sat around and occasionally spoke), while Vanessa (who underwent a Clothing Switch with Candace to Lampshade the whole thing) tried to tell her mom. He even expected Perry to show up ("Hey, where's Perry the Platypus?"), but Perry was unable to get to Major Monogram because of a pet-cone. Meanwhile, Phineas built a machine that would spread a rainbow over The Entire TRI-STATE AREA!!!, only for Perry, who was unable to see past pet-cone, hit the self-destruct button on it. He sneezes ("Bless you, Perry the Platypus!"), and Phineas removes the cone. Perry then rushes to the docks, where Doofenshmirtz's city has sunk (before Vanessa could get her mom there). Doof delivers the "Oh, there you are Perry The Platypus." and Candace and Vanessa meet up at a store, and presumably switch clothes offscreen.
An episode of Rugrats uses a variation on Clothes Make the Maniac. Whilst in the park, Chuckie and Angelica manage to switch shoes. Chuckie slowly becomes more bossy and condescending to poor Tommy, while Angelica mellows out and become afraid of everything. However, the whole ordeal turns out to be All Just a Dream that Tommy had after hearing his dad comment 'I'd hate to be in that guy's shoes,' whereafter Angelica lied and said that if you put on someone else's shoes, you become that person.