Butt Biter

No need for such a biting response, Calvin.

"Bitten in ze butt!
Got an awful tear!
Took a little nibble from my derriere!
I will get you in ze end, dog!
You'll regret you bit me, chum!
Ooooh, I am so irritated I got bitten in ze bum!"

—Les Miseranimals, Animaniacs

Animals are one of nature's beauties of the earth. Some are cute and cuddly while others can be rather shy. However, there's this kind of animal, the biting kind that can literally bite you on the butt if you're not careful.

This breed of animal is what's known as a Butt Biter, they can be dogs, cats, pigs, ferrets, any other animal you can think of. The next time you come across this type of animal, beware.

Often results in the butt-biter making off with a piece of trouser fabric, leaving a hole behind through which Goofy Print Underwear may be visible.

Subtrope of: Amusing Injuries and Literal Ass-Kicking.

Compare: Pinching Pain, Animals Hate Him. Not related to Boob Bite.

Examples of Butt Biter include:

Anime and Manga

Not really getting bitten, but JP from Digimon Frontier gets pinched in the butt by a crab.
Half Prince had this happen to the main character in the first chapter.
Happens to King Dedede near the end of that episode of Kirby: Right Back at Ya! with the Dedede dolls as a result of one of said dolls being bitten by a mole shortly after being buried in the ground as an attempt to prevent it from menacing anyone. Dedede then proceeds to thrash around, causing the doll to attack the innocent one last time before Kirby swallows the doll, causing Dedede to for some reason fly off into outer space and fly past a planet shaped like him.
A dog does this to Shinobu in Love Hina, what makes it worse is that this is after she had already failed some tests at school. The same dog also bites Keitaro earlier on in the manga.
In an episode of City Hunter, a guard dog bites Kaori, ripping at the same time the seat of her pants.
Believe it or not, Chris actually fell victim to this trope once, at the end of the Moses episode of Superbook. Chris tried pinning the blame for breaking his father's vase on his dog Ruffles. Ruffles, not taking too kindly to being his scapegoat, began chasing after Chris, until halfway down the stairs, when she clearly looks like she just bitten him on the rump.
Yu-Gi-Oh! GX Jim Cook's companion crocodile Karen bit Kenzan and Shou on two different occasions.

Comics

De Cape et de Crocs: Justified in that the main characters are a wolf and a fox, and are tied up. This even leads to a sadly-untranslateable Double Entendre: the others are using various puns based on what body part is being attacked (forehead, eye, throat, the guy getting bitten stops short of saying he's being sodomized).
In Dennis the Menace UK, Gnasher does this to the postman. One story revealed he had a collection of ripped seats from blue uniform trousers.
Calvin and Hobbes: Pictured above, Calvin got bitten by a fish while he was out fishing.
In the Nintendo Power comic of Super Mario Adventures, both Mario and Luigi, while trapped inside of a haunted house, had to deal with BUM-BITING BOO-BUDDIES!!!
Happened to Rat in this recent Pearls Before Swine strip.
The Bzz Fly in The Smurfs comic "The Black Smurfs", who causes Smurfs to turn black by biting them in the tail. Also the purple fly in the Animated Adaptation counterpart "The Purple Smurfs".

Film

The Mask. While wearing the title item, Milo the dog bites one of Dorian Tyrell's Mooks on the bottom.
Another Jim Carrey movie providing an example was How the Grinch Stole Christmas, which Max does this to persuade The Grinch to save Cindy Lou in the post office.
Implied in Aladdin. We see Prince Achmed with a bite off his pants, and then we see Rajah the tiger with fabric on his mouth.
In The Aristocats, Edgar is attacked by angry guard dogs Napoleon and Lafayette, who bite off the seat of his pants. They even discuss it beforehand:

Napoleon: Now you go for the tires, and I go right for the seat of the problem.
Lafayette: How come you always grab the tender part for yourself?
Napoleon: Cause I outrank ya, that's why!

Max the sheepdog actually takes a bite out of Vanessa's behind toward the end of The Little Mermaid just right before she reverts back into Ursula.
In Inspector Gadget, Brain the intelligent dog bites the evil Dr. Claw, ripping off at the same time his blue boxers (no nudity, it's a Disney movie).
Disney, once again, with one of the dogs from Homeward Bound: The Incredible Journey II: Lost in San Francisco tearing off a dognapper's underpants.
It happens to Skinner and Le Pelt in both movies based on One Hundred and One Dalmatians.
In the Disney independent film The Duke, a dog takes her revenge towards her owner by biting her bottom.
The sorceress played by Kathleen Turner in A Simple Wish gets bitten on the bum by her own assistant, changed into a dog earlier in the movie.
Even Curly wasn't immune to the bite to the seat of his pants from a US Marine Corps bulldog in the episode "Higher Than A Kite"... especially when a picture of Hitler was stuck on Curly's butt!
A zombie attacks a cheerleader by biting her on the ass in Return of the Living Dead: Rave to the Grave.
In the Surreal Horror film Hausu, Mac's decapitated head bites Fanta in the rear.

Literature

In Extinction (War of the Spider Queen series) a warrior told how an upstart mage of his House once tried to "teach him his place" by polymorphing into a riding lizard (as in, a camel-sized raptor) and saddling. This didn't quite work as planned, in that the transgressor was unable to sit for some time, blaming it on a "riding accident".
In the Dresden Files book Changes Mouse the Celestial Foo Dog of the titular wizard threates the Leanansidhe, Harry Dresden's Faerie Godmother with this if she does not behave. Lea actually seems a slightly taken aback.

Live-Action TV

Xena: Warrior Princess is bitten on the arse by Ares's dog in the episode "Old Ares has a farm."
In the David Lynch/Mark Frost soap-opera On the Air, a dog bites the large backside of the angry assistant of an actress.
The unlucky Raven from That's So Raven gets her booty bitten twice during a costume party.

Video Games

In Conkers Bad Fur Day, Conker mounts a Raptor and uses it to actually bite chunks out of a giant caveman's butt. It Makes Sense in Context.

Western Animation

Blitz of Road Rovers often does this to the bad guys. Hearing him brag about gets a LOT of wry looks from the others.
Seen It a Million Times in Looney Tunes, MGM Cartoons, etc. Often the dog will hang on for a very long time, like hours.
- Hanna-Barbera has two dogs known to follow the trope: Muttley and Precious Pup. Dino from The Flintstones also had been known to give a nip or two to Fred's behind from time to time
In the Tex Avery cartoon "Three Little Pups" the wolf is bitten in the butt by a bulldog. He goes to a changing screen and hangs up his pants... with the dog still attached. A few scenes later he walks by the screen again, and the dog is still there! Wolf tells him...

Wolf: Okay, break it up son. Jokes over ya'hear?

One Rita and Runt short from Animaniacs was a parody of Les Misérables, and had a character who'd been bitten break into song about it (lyrics shown).
Tulio from Road to El Dorado was bitten in the rear by a jumping piranha in the 'traveling the jungle' montage.
- He also claimed to suffer the same treatment from Altivo the horse.
In Brother Bear, a dog tied to a post bites Denahi on the butt while he flirts with some women.
It happens in some Woody Woodpecker's cartoons, generally to a dumb dogcatcher or the mean-spirited Miss Meany.
Happens to Candace in an episode of Phineas and Ferb.
In the Rugrats episode "The Smell of Success", the bully that has been bothering Chucky and Tommy the entire episode gets knocked backwards into an anthill by Chucky's sneeze. The ants crawl down the back of the bully's shorts and bite his rear end, prompting him to run off.
Referenced on The Simpsons

Homer: Lisa, remember that postcard Grampa sent us from Florida of that alligator biting that woman's bottom?
Bart: Oh, yeah, that was brilliant!
Homer: That's right, we all thought it was hilarious. But it turns out we were wrong: that alligator was sexually harassing that woman.
Bart: And the dog in the Coppertone ad? Same deal, Dad?
Homer: Well, that's kind of a grey area.

Besides the aforementioned purple fly, there's also the Japanese slumber bug in The Smurfs Season 9 episode "Papa's Big Snooze".
In the Beavis and Butt-Head episode, "Coach Fishing", the boys were watching a show about piranhas when one of the fishes bites the speaker in the butt. Though cut away, blood was seen around the man, leading Butthead to quip.

That fish just ate his butt

.

Real Life

Police dogs can actually do this to criminals that they pursue.
Aggressive horses are known to do this, particularly when they have no other means of expressing their displeasure.
This camel.