Favouritism Flip Flop

Bob has a great plan! He tells Charlie about it, but Charlie hates it. That is, until Alice comes along and says that she loves the plan. Charlie instantly switches, telling Alice that he loves the plan too, and they jump to go carry the plan out, whilst Bob stands there, surprised and vaguely insulted.

A slight variation is when Charlie is against the plan until Bob says it's about something Charlie likes, whereupon he's all over it.

Standard quick gag in many series, especially Slice of Life. Subtrope of Like a Weasel. Compare Glad I Thought of It, where Alice and Charlie are the same character.

Anime and Manga

 * Anri from Sasami Magical Girls Club is like this toward Tsukasa, often showing disdain for things until she sees that Tsukasa is interested, then immediately supporting whatever that thing is.

Comic Books

 * In a Zits comic, Jeremy's mother gives him a fashion suggestion and he complains. Later, his girlfriend gives him the exact same suggestion and he simply says "Okay."

Film

 * Monster House
 * In Father of the Bride, the daughter dismisses her father's suggestion that she put on a coat because it's cold, but when her new fiance immediately suggests the same thing, she does.
 * In one of the Lethal Weapon movies, Murtaugh's daughter comes to him and Mel Gibson's character and shortly engage in a discussion about alcoholic consumption at her age. Her father says she shouldn't drink, but she brushes him off. However, when Gibson's character asks the same, she - having a crush on him - promises to take his advice and whole-heartedly agrees with him.
 * There may be similar events considering the three throughout the four movies.

Live Action TV
"Jayne: Don't know these folks, don't much care to.
 * My So-Called Life
 * Parodied in a "Moody's Point" segment of The Amanda Show.
 * The variation occurs in Firefly in "Heart of Gold".

Mal: They're whores.

Jayne: I'm in."

"The Doctor: I won't do it. Whatever it is, I refuse.
 * The variation also occurs in the Doctor Who serial Genesis of the Daleks:

Time Lord: Daleks.

The Doctor: Daleks. Tell me more."

New Media

 * In an episode of Sailor Moon Abridged, Serena scoffs at Luna when she tells her that she can defeat the Monster of the Week by believing in herself. Then, Tuxedo Mask tells her the exact same thing and she listens to him because "he said it with a sexy voice."

Theater
"Ruth (to Frederick): Remember Ruth, your Ruth, who kneels before you!
 * How to Succeed In Business Without Really Trying has an instance of this; where the nephew of the president suggests an idea, which the president hates; but when the main character suggests it, the president loves it. (In fact, the only reason the main character had the idea in the first place was because the nephew told it to him after the initial failed suggestion, deliberately trying to discredit him.)
 * From The Pirates of Penzance:

Pirates: Yes, yes! Remember Ruth, who kneels before you!

Frederick: Away, you did deceive me!

Pirates: Away, you did deceive him!

Ruth: Oh, do not leave me!

Pirates: Oh, do not leave her!

Frederick: Away, you grieve me!

Pirates: Away, you grieve him!

Frederick: I wish you'd leave me!

Pirates: We wish you'd leave him!"

Webcomics

 * Inverted in Order of the Stick, where Belkar's approval of Roy's plan "fills [him] with shame" (doesn't stop him from carrying it out, though).

Web Original
"Penny: It is so dumb that we've been coming here so long and never spoke.
 * Dr. Horrible's Sing-Along Blog:

Billy: I know. All those months of doing a stunningly boring chore...

Penny: I'm a fan of laundry.

Billy: Psych! I love it."

Western Animation
"Caleb: It's bad enough I've got to hang a towel from my pants and ask people if they want extra apricot sauce, I'm not gona go further demean myself by jotting down the ramblings of a love-struck girl.
 * In the Adventures of Sonic the Hedgehog episode 'Birth of a Salesman,' Scratch and Grounder initially express their distaste for Wes Weasley. When Robotnik then refers to him as '[Robotnik's] kind of guy,' the two robots immediately backtrack and claim that they also like him.
 * The variation occurs in the WITCH episode 'The Princess Revealed' between Caleb and Hay Lin:

Hay Lin: If you hide behind the mangrove tree and take notes, I'll do your next shift.

Caleb: Interesting..."