Hilarity in Zoos

Alice and Bob decide to take a trip to the zoo with their friends Charlie and Dave. It starts off as a fairly uneventful occasion, then Dave gets his hand bitten trying to feed the monkeys (despite the incredibly obvious "Please Do Not Feed the Monkeys" sign). Then Charlie accidentally breaks a cage in the Reptile House, releasing a 50-foot anaconda. While the authorities are trying to deal with that situation and people are rushing out in panic, Alice accidentally gets knocked into the bear pit, and now it's up to Bob to figure out some way to rescue her...

Hilarity in Zoos is, essentially, just that sort of situation. Whenever a group of characters goes to the zoo, it's almost a given that something is going to happen. It might be played for either comedy or drama, but inevitably, as you might expect, An Amusing Circumstance of Some Sort Occurs.

Anime

 * Katekyo Hitman Reborn episode 14, "First Date!? Hell's Zoo": Highlights include having to recapture all the animals after Lambo blows up all their cages, and Ryohei testing his strength "to the extreme" by fighting a bear—at a video game.
 * In Sora no Otoshimono, Ikaros, at Nymph's suggestion, frees all the animals from their cages. That would be bad enough itself, but Tomoki ends up getting stripped and is believed to be the one who freed them. This gets so out of hand that Barack Obama himself finds it a global emergency.
 * An episode of Keroro Gunsou had Keroro sneaking into a zoo after-hours with a ray-gun that turns animals into humans, with the hopes of recruiting some of the transformed animals as soldiers for his invasion.
 * Yotsubato: Yotsuba punches a goat, freaks out on meeting an owl, and is mesmerized by the elephant.

Comics

 * Two examples from The Punisher: the first, when Ma Gnucci and her Mooks pursued Frank into a zoo, and he, without much in the way of weapons, used the animals to fend them off, culminating in a darkly hilarious fate for Ma Gnucci herself. The second time is when a mook that Frank needs for information tells him about how the made man he was working for antagonized a monkey in a zoo. Said monkey proceeded to rip the guy's junk off and tossed it away, where it eventually got eaten by a vulture.

Film

 * Anchorman has the scene where the Channel 4 News Team goes to the San Diego Zoo to investigate Yet Another Baby Panda. Highlights include Ron jumping into the Bear Pit to save Veronica from certain danger (without thinking his plan all the way through) and a rival news anchor getting his (one remaining) arm ripped off.
 * Fierce Creatures takes place almost entirely at a zoo, so naturally they take advantage of it.
 * Old Dogs: Three of the protagonists try to sneak into a zoo and end up tangling with a gorilla and killer penguins.
 * Baby's Day Out : The whole sequence where the three bad guys try to retrieve the titular baby from a gorilla in a zoo. Hilarity Ensues as they get pwned by the gorilla in each of their attempts.

Literature

 * Harry Potter and the Philosopher's / Sorceror's Stone: Harry's accidental wizardry let a snake out of its case and trapped Dudley in it.
 * Not exactly zany, but in one Animorphs book they go to the zoo and end up having to rescue a kid who falls in the crocodile pit. Rachel ends up discovering she's allergic to crocodile DNA (It Makes Sense in Context) It ends with a grizzly bear fighting a crocodile on national TV while scaring the crap out of an infuriatingly annoying teen star.
 * Cassie's mother is a vet at the local Amusment Park/Zoo and the kids regularly go to get there to get new morphs since the very first book. Probably the most insane event was the time Tobias needed a Dolphin morph and decided to get it during the water show (his plan was to fly in and land on it's back, being that he's a Red-Tailed Hawk and not a human). Much to his horror, the Dolphin was spooked by this and begins to get very hyper, the reverse of the norm when they acquire new morphs.
 * Dr. Seuss's If I Ran the Zoo.

Live Action TV

 * Malcolm in the Middle had a zoo episode. Highlights included Hal being bitten on the face by a tarantula during a demonstration, and Malcolm and Dewey getting trapped in the tiger pit.
 * The main characters of The Mighty Boosh are zookeepers, and some episodes deal with a problem at work.

Music of Note

 * The song "Monkey Punk" (made famous by Dance Dance Revolution) is about a group of kids who go to the zoo. One sticks his tongue out at the monkeys, which upsets them, and so one monkey retaliates by stealing his ice cream and making everyone laugh at him.

Newspaper Comics

 * On Calvin and Hobbes, Calvin's family goes to the zoo and he gets lost. Surprisingly, not much actually happens beside that, although Dad does run a little faster when he imagines Calvin going into the tiger pit because he likes them so much.

Western Animation

 * There was an episode of The Replacements that had this as the plot. Riley replaces the zookeeper with someone who, she thinks, will take better care of the animals. She (the replacement) lets all the animals free. At the end of the episode, the animals are allowed to run free in a Golf Park, making it Hilarity In Golf Parks.
 * There's the extremely controversial Simpsons episode "Homer vs. Dignity", where Homer gets molested by a panda.
 * Reverend Lovejoy rescues Ned Flanders from the baboon exhibit.
 * Another episode has Bart taken in by a mother gorilla in the zoo.
 * There is a very early Looney Tunes cartoon featuring Egghead (the precursor to Elmer Fudd), who eventually gets eaten by a lion—but we also take a look at all the other zoo animals as well.
 * There's another featuring Pepe Le Pew one where the animals react to his smell.
 * And a third with Sylvester chasing Tweety all over a zoo.
 * An episode of DuckTales did this, when the Beagle Boys steal Gyro's furniture mover ray to steal Scrooge's money. Huey, Dewey, and Louie eventually find them but get chased away by the Beagle Boys, into a zoo. Hilarious antics include a gorilla being teleported between two lovers about to share a kiss, and an elephant being teleported in front of an elevator.
 * There was the episode of Ren and Stimpy in which they dressed as monkeys and lived at the zoo.
 * One episode of King of the Hill deals with Hank being raped by a male dolphin at a Sea World-esque park.
 * A vintage Popeye cartoon has Swee'pea cheerfully running loose among a zoo's animals with Popeye in frantic pursuit. After Popeye rescues Swee'pea, he gives him a cute monkey-on-a-stick toy that makes him scream in terror, just as Olive comes to pick him up.
 * Beavis and Butthead join a zoo tour, hoping the guide will talk about the animals "doing it", which she only does after they leave in boredom. While they're in the reptile house there's a momentary power outage that gets them in a panic, and when the lights come back on they're in a compromising position, inadvertently holding each others...snakes.