Cute Is Evil

Oh, monster of so little size... is that a parasprite before my eyes?

—Zecora, My Little Pony: Friendship Is Magic

Cute Is Evil happens because people (both In-Universe and in Real Life) slide to the cynical end of the Sliding Scale of Idealism Versus Cynicism. It is also related to the phenomenon of people losing the ability to think critically around cute things - thus being an ideal cover for a Person of Mass Destruction.

Parents and older siblings tend to hate cute. Brothers especially hate cute, as it is contrary to more manly forms of expression. Male television executives in charge of programming try to keep girls liking cute as long as possible.

Cute is often evil in Darker and Edgier works. In extreme cases, cuteness is a sign of someone being an Uncanny Valley inhabitant or Eldritch Abomination.

A frequent component of Subverted Innocence tropes such as Cute and Psycho, Corruption by a Minor, Killer Rabbit and Crap Saccharine World.

Very often the core of morally questionable, if not outright malevolent, children types such as the Creepy Child, Kids Are Cruel, Deliberately Cute Child, Spoiled Brat, Evil Orphan, Little Miss Con Artist and especially the Enfant Terrible, who exists mostly to enforce this trope.

If they succeed at causing death and destruction, this trope will likely overlap with Grotesque Cute.

Contrast Beauty Equals Goodness and Kawaisa. Compare Beauty Is Bad, a milder form, and Adorable Evil Minions.

Examples of Cute Is Evil include:

Anime and Manga

Majin Buu, the final major villain of Dragonball Z. The form that our heroes encounter first is an Ugly Cute, fat pink humanoid of mass destruction with the mentality of a toddler. He also has a massive craving for sweets. Sweets made by zapping his victims with his head antenna and transforming them into foodstuffs that are still completely conscious as they are being eaten.
Iron Maiden, but her alignment is more Lawful Stupid than evil.
Pokémon has featured both an evil Teddiursa and an evil Togepi.
Digimon Frontier Lucemon anyone?
The Amazon Quartet and Sailor Iron Mouse from Sailor Moon.
For all their creepy qualities no one can deny that Black Lagoon‍'‍s Hansel and Gretel are cute.
Kyubey of Puella Magi Madoka Magica. When you first see it, it's the most adorable thing in the world, but the blank red eyes and unchanging Cat Smile just get creepier and creepier every time you look at it. There is a very good reason for this. This is also an invocation of this trope, as Gen Urobuchi specifically asked character designer Ume Aoki to make it "as cute as possible."
- And there's Charlotte, who's incredibly adorable until you see her true form...
The Puchuus from Excel Saga.
Deadman Wonderland is set in a prison that is also a theme park. The inmates stage shows for the visitors. This is mostly promoted by the... er... Promoter, who seems to run the place and is a Psychopathic Manchild who loves to put cute, evil props everywhere.
In D.Gray-man, The Earl and Road Kamelot seem to have a theme like this going on.
Umineko no Naku Koro ni has at least 3 characters like this, or 2 if you consider an independent avatar and her master as a single being.
Popotan being what it is, it still provides an example in the form of the little girl from episode 4. She appears to be a normal child at first, but is actually a ghost who wishes to trap people where she can be with them forever.

Film

In the first Scooby-Doo live-action movie, the villain is Scrappy.
In the Star Trek spoof Galaxy Quest, the crew stumbles upon a cuddly group of child-like aliens, which they watch from afar. They almost fall for it... until the creatures show their true colors and eat a wounded member of their own species.
- Of course, tag-a-long crew-member Guy Fleegman doesn't fall for it for a second, but that's because he watched the TV show and knows the drill.
The Mini Pufts from Ghostbusters: Afterlife. These teeny-tiny versions of the Stay Puft Marshmallow Man (from the original movie) are adorable and usually just mischievous, but are, in fact, minor manifestations of Gozer (the Big Bad of the original movie) and loyal to Gozer's other minions.

Live-Action TV

This trope is inherent to many a Power Rangers monster, but also some villains. If the Five-Bad Band has a small child, expect her to be The Starscream.
Star Trek: Tribbles are cute, furry little puffballs who lovingly purr when someone (other than a Klingon) holds them, but they eat anything they perceive as edible - such as grain or anything humans eat - and multiply when they eat their fill; technically not evil, seeing as they don't know any better, but they can be very destructive if even a few of them get into a storehouse or crop silo.

Literature

Baby Veil in Outcast of Redwall sends Bryony into paroxysms of Cuteness Overload, even when he's actively in the process of biting her. Unfortunately for him, it doesn't work when he's in his teens and starts playing with poisons.

Music

"I'm sick of you little girl and boy groups/All you do is annoy me/So I have been sent here to destroy you . . ."

Newspaper Comics

Nermal in Garfield has attracted serious Hatedom for being cute and preoccupied with his own cuteness.

Tabletop Games

The julajimus from Dungeons & Dragons, a monster created by Tharizdun's dark magic. Its true form is clearly not cute at all (it's a huge demon that looks like a monstrous ape) but it has the ability to take the form of a cute kitten, rabbit, or other harmless animal. Humanoid races have legends of this creature that parents use to scare their children; the story starts with a child finding an adorable kitten, who his parents refuse to let him keep. The story ends with the child disobeying his parents and sneaking it into his room, only for it to transform into its true form of a julajimus and devour him. The moral is very clear, but the julajimus is a very real monster, as far as the game world is concerned, and much like all of Tharizdun's evil creations, very dangerous.
Magic: The Gathering has an Unglued card called Infernal Spawn of Evil. With a name like that, you're expecting some sort of demon, perhaps an Eldritch Abomination. It's...a mouse enjoying hot cocoa.
- In the sequel set, Unhinged, they introduce Infernal Spawn of Infernal Spawn of Evil, which is the same mouse, holding its cocoa in one forepaw, and its baby mouse in the other forepaw.
- On a more serious note, the non-joke set Ice Age included the Hyalopterous Lemure, which is pretty cute for a black card. Reportedly, the artist had never heard of a lemure (a minor evil spirit) and drew a lemur instead.
Very literally in the horror-themed Munchkin Bites, where a fearsome high-level monster simply titled "The Evil" looks a whole lot like... a fuzzy little kitty cat.
- It's a reference to the Sluggy Freelance entry below.

Video Games

A lot of monsters in RPGs, but especially Tonberry (If you're in any way experienced, it can manage a One Hit KO.) and Cactuar (not so bad when they can just do 1000 damage, but they often can do 10000) in Final Fantasy.
Lakitu in most Super Mario Bros. games. He rides around on a smiling cloud, has cute glasses, is harder than hell to kill, and drops eggs on you that hatch into spinies when they hit the ground. The obvious exceptions are Super Mario RPG, where he's just another enemy, and the Kart games, where he actually grabs you if you fall off the track.
The main villains of Razes Hell are an army of cute creatures that decide to wage a genocidal war against the ugly creatures of the world.
Marx from Kirby. When you think all of the good characters in Kirby are good and the baddies are ugly, you are all wrong. Marx starts from being a really cute, armless puffball. He bounces on a really colorful beach ball and has a jester hat. Later he turns out to a villain after the mistaken 'end' of the game. In the sequel, Kirby Super Star Ultra, he turns to the freaky-looking Marx Soul.
- Aside from Marx, there is also Scarfy, though Waddle Dee won't count, since they're just innocent, carefree creatures.
B.B. Hood from Darkstalkers.
The balloon Pokémon Drifloon looks cute, but it tries to kidnap children.
- Let's also not forget about Litwick, which pretends to be a helpful guiding light which in reality is attempting to steal your life energy. Its evolutions are just as cute and even worse.
In Kingdom of Loathing, one of the most evil, foul, reprehensible creatures of in the world is... seals. Adorable little seals. Naturally, one of the character classes is the Seal Clubber.

Web Comics

Sluggy Freelance K I T T E N. Now in a compiled volume called "Little Evils", with Bun-bun featured front and center, brandishing his knife.

Western Animation

The Jimmy Neutron episode "Attack of the Twonkies" is all about this—cutsie little fuzz balls morph into POINTY BALLS OF TERROR when they hear music.
On Total Drama Island, Duncan is afraid of Celine Dion music store standees.
On Robot Chicken, in a Dragonball Z parody, the characters go to the North Pole. Their enemies? Little Drummer Boy, the Nutcracker, and Composite Frosty/Santa Claus. But the Big Bad is Mrs. Claus.
Baby Doll of Batman the Animated Series looks like a cute little girl but is a really a psychopathic adult.
In Hoodwinked, the villain is the bunny rabbit that follows Red around all the time.
- In the sequel, those dang "innocent" children they were trying to find.
Jimmy, the effeminate squeaky kid on Ed, Edd 'n' Eddy, generally isn't the most affable sort. But he has on occasion demonstrated Chessmaster prowess—and ruthlessness—to rival Machiavelli.
Kitty, a cute white cat who happens to be a minor villain, from The Powerpuff Girls.
- "Sweet 'N Sour" should probably be placed here.^{[dead link]}
The Woodland Critters from South Park.
Adam Lyon from My Gym Partner's a Monkey has a run-in with the "Petting Zoo Kids" in one episode. These are a clique of doe-eyed miniature animals that use cuteness as a cover to pilfer unsuspecting victims who succumb to a "huggie". Adam loses all of his clothes following a few encounters and losing his good judgment around them. Eventually he turns the tables by cornering and shaving off their fur, removing their cute charm.
The Adventure Time episode "Conquest of Cuteness".
- Of course, it's kind of Subverted in that the Cute King and his minions are Ineffectual Sympathetic Villains.
- Let's not forget Memow, the little assassin.
Lotso Bear from |Toy Story 3.
On Drawn Together, we have a Strawberry Shortcake Expy, whose people almost completely exterminated Wooldoor's. Since nobody but the two characters had ever heard of this, we can assume they have been as successful at denying it as the Turks have been in denying the Armenian genocide. Oh, and she tries to kill Wooldoor.
The Flores from the My Little Pony episode "Fugitive Flowers" look like cute and harmless talking flowers, but are really monstrous invasive weeds who trick Posey into protecting them from the creepy-looking Crabnasties who are trying to capture them, then proceed to transform and go on a rampage.
- My Little Pony: Friendship Is Magic has the parasprites from "Swarm of the Century". While they don't seem to be actively malicious, they're still adorable, multicolored bug/fairy critters who breed rapidly and devour all the food they can find. Basically, they are the unholy spawn of Tribbles and Piranhas.
Clare of Titan Maximum, whose bio states "she loves cute things and desires to be the cutest thing in the entire solar system! Oh, and by the way, she’s completely evil."
The Gigglepies from The Fairly OddParents, who hypnotize people with their cuteness in order to sell their merchandise and destroy planets.
The Squirrelanoids (as they are called) from the 2012 version of Teenage Mutant Ninja Turtles. Initially, they look like cute, adorable squirrels, and the Turtles and Splinter think so until they discover that they reproduce via Orifice Invasion. Of course, a few hours after doing so they grow into monsters that are a bizarre cross between squirrels and xenomorphs, not very cute at all.