Animal Stereotypes. Rats are sneaky and mean, mice are cute and nice, porcupines are grumpy and prickly, beavers are hard-working, and so forth.
Squirrels (and their close relatives, chipmunks) are, however, mostly seen as hyperactive animals who either love to play pranks and mess around with people, or are just off-the-walls crazy. They will run around stealing nuts from people — and then drop these nuts on people's heads, driving them nuts. They also have the bad habit of crawling into people's clothing, and are among the arch-enemies of dogs, often because the dogs are fed up with their antics. Bonus points if they have very short attention spans, too.
It's easy to see why these furry critters have such traits associated with them: squirrels and chipmunks are very jittery animals in real life, moving about in short, twitching movements, and taking off to the nearest tree at the slightest sign of danger. Their recognizable constant chattering heard in media also gives the impression of manic cackling, as if they just pulled another prank on some hapless bloke. They also tend to cache food and then forget about it, which fuels the "short attention span" stereotype.
Note: Just because a character is a squirrel or chipmunk, it does not mean they automatically qualify for this trope. The example also needs to describe how the character is a troublemaker and/or a cloudcuckoolander.
Subtrope of Animal Stereotypes. Also compare Rascally Rabbit, another small, furry animal that's often a trickster and prankster. The Trope Namer is the Tex Avery cartoon Screwball Squirrel. The trope formerly known as "Screwy Squirrel", about crazy, malicious prankster characters that are usually not squirrels, is now split between The Gadfly, Troll, The Prankster and Cloudcuckoolander.
- Pokémon: Dawn's Pachirisu, an Electric-type Pokemon based on a squirrel, has a very playful and hyperactive personality, running around with boundless energy. Dawn had a difficult time controlling it at first.
- Mutts: Bip and Bop are a duo of mischief-making squirrels who enjoy bonking people in the head with acorns.
- Ice Age: Scrat is a prehistoric squirrel whose nuttiness mostly manifests in a single-minded obsession with an acorn that he keeps losing due to all sorts of crazy circumstances. Scratte, his Distaff Counterpart from Ice Age 3: Dawn of the Dinosaurs, fits the "screwy" part of this trope better, flirting with Scrat just to screw him over and steal his acorn.
- Over the Hedge has the extremely hyperactive squirrel Hammy, who acts as a Cloud Cuckoolander Manchild and is obsessed with sugar. At one point, he goes into Caffeine Bullet Time after simply drinking a soda.
- The Sword in the Stone: When Wart and Merlin temporarily transform themselves into squirrels, they encounter two extremely flirtatious and pushy females who just won't stop despite their protests. As Wart flees from the girl squirrel they wake up Archimedes, who derides them as "You screwy squirrels!"
- Borgel: Inverted in one of Uncle Borgel's fables, "The Tale of the Moose and Squirrel". The fable features mischievous animals, but the story pulls a Stereotype Flip between this trope and Moose Are Idiots, thus the moose is The Trickster who tries to steal the squirrel's acorns, while the squirrel is a simple-minded Straight Man who doesn't want any trouble.
- Alvin and the Chipmunks: The chipmunks often act like mischievous children, getting on the nerves of their manager / surrogate father Dave Seville. Alvin is their trouble-making leader, whereas the nerdy Simon and naïve Theodore usually only make trouble by following Alvin. In their original music act, they mess up the recording at the end by demanding to do the song again and quarreling with Dave and making a mess. The characterization is carried over to the various animated and live-action adaptations.
- Conker's Bad Fur Day: Conker himself zigzags this trope. He's alcoholic, greedy and violent, but he's also the Only Sane Man in his own game, which kinda downplays the notion that his troublesome personality comes from the fact that's he's a squirrel (instead of a natural result of dealing with a Crapsack World).
- Pokémon Sword and Shield: Skwovet and Greedent are a line of greedy squirrels who make trouble by stealing and hoarding food and berries. There's a minor sidequest in the game with a Skwovet making trouble in a hotel.
- Happy Tree Friends:
- Nutty the bright green squirrel is pretty much as insane as you'd expect with a name like that, further accentuated by his hyperactiveness, a Mad Eye, and a vocabulary consisting entirely of manic laughter. His signature trait is his love for anything made out of sugar, which he sometimes outright places before common sense (resulting in gruesome Cruel and Unusual Deaths... plural).
- Averted with Giggles the chipmunk, who doesn't display any of the defining traits of this trope, and is more of a girly rose-furred sweetie.
- Animaniacs: Slappy Squirrel is a grouchy, elderly squirrel who whacks people with her purse. In her youth, she was a gender-flipped Expy of Screwy Squirrel, a hyperactive prankster (and quite a looker at the time). Her age slowed her down, but she never lost her malice. Her nephew Skippy is the exact opposite, hyperactive but naive and innocent.
- Big Buck Bunny has a trio of squirrels who start playing mean-spirited pranks on the eponymous Gentle Giant rabbit and then get their comeuppance when said rabbit gets dangerous.
- Classic Disney Shorts: Chip 'n Dale are a duo of chipmunks who often get into an Escalating War with Donald Duck. Who starts the fight depends on the cartoon: sometimes they respond to Donald's jerkass behavior, but sometimes they just start messing with him for no apparent reason. Averted with their Chip 'n Dale Rescue Rangers version, who are crime-fighting heroes.
- Screwy Squirrel, a recurring character in Tex Avery's cartoons introduced in the Trope Namer cartoon, Screwball Squirrel, is a prankster who messes with innocent people for no good reason.
- Phineas and Ferb: In the episode "Comet Kermillian", Suzy Johnson throws a nut into Candace's pants, grabbing the attention of two hungry squirrels. As Candace jumps around to get rid of the squirrels in her pants, she creates an Accidental Dance Craze that is the Trope Namer for Squirrels in My Pants.