A smile is supposed to be a reassuring expression, indicating happiness and complete absence of angst and danger. If someone's smiling, it means all is well with the world...
...unless it's a Cheshire Cat Grin, which always denotes that someone's in for it.
The Cheshire Cat Grin is an expression made by a Trickster who's up to something, and "something" never bodes well for the person he or she is smiling at. Usually, it involves their total humiliation — occasionally it involves mortal danger. A typical scenario runs something like this:
Character A: Wait, we need someone to dress in a bikini, swim across a river full of piranhas, placate the pride of man-eating lions with the power of dance and steal the sacred ruby out from under Lord Evil's nose? Who's the poor fool who's gotta do all that? Character B:(grins at character A) Gilligan Cut to character A dressed in a bikini swimming across a river full of piranhas to placate the pride of man-eating lions with the power of dance so he can steal the sacred ruby out from under Lord Evil's nose.
Generally, this is drawn as a smile with far too many teeth on display, where the mouth doesn't match up with the eyes, going practically from ear to ear. For example, the mouth may be a broad grin, but the eyes definitely have a wicked gleam in them. It occasionally has sexual connotations, particularly when there's a predatory quality about the grin.
Strangely, it's usually done by heroes who have a Zany Scheme in mind, rather than by villains, who tend to prefer the Psychotic Smirk or the Slasher Smile. Heroes and heroines who are slightly eccentric — or slightly deranged — favour the Cheshire Cat Grin. If it's an anime, expect a Cat Smile instead. Common trait for The Gad Fly and serves as a warning that they're going to pull their antics on someone. If this smile is a permanent feature, it's a subtrope of Frozen Face; if it's cut into the character's face, it's a Glasgow Grin. Shares living space with The Un-Smile.
If you ever see someone with the Cheshire Cat Grin in real life, vacate the premises before you can discover what they're smiling about. Or, for that matter, how their face manages to do that.
Although Alice's Adventures in Wonderland is considered the Trope Namer, the term "grin like a Cheshire cat" was actually common in Britain during Lewis Carroll's time. The origin is uncertain; the most likely sources are some Cheshire cheeses that were molded into the shape of smiling cats, and a famous inn in Cheshire that had a painted grinning lion on the door.
Gengar, from Pokémon, tends to have either this or a Slasher Smile depending on how it's drawn. Either way, it is constantly worn and only twice in the anime Gengar actually frowned.
See the example under Video Games for a time when he does frown.
Dee Laytner, from the FAKE manga and anime, is a good example of a grin with sexual overtones, while he's plotting how to seduce Ryo. Occasionally, Dee's expression is downright scary, and it leads Ryo to comment, "You're grinning like the Cheshire Cat." Here, have a look.
Washu of Tenchi Muyo!!, usually right before she's about to stuff Tenchi into some machine or another.
Ichihara Yuko from Xxx Ho Lic has a grin that can roughly be summed up in words as: "Not only do I know something you don't know, but it's going to bite you in the ass in a veryamusing fashion." Despite this, it's when she appears serious that should really scare Watanuki. This is because Yuko's Cheshire cat grin simply means she's going to make him do all the laundry, whereas the latter expression is usually a forecast of man-eating crow demons or similar.
Deviant genius Hiruma from Eyeshield21 has this as one of his default expressions, to the point where those new to the series — or complete non-fans — can identify him as 'the one with the teeth.'
Road Kamelot of D.Gray-Man, several times. Along with some of the AKUMA. Hell, the Earl probably counts as well.
Haruko of FLCL, usually when she's about to be entertained, between the Cat Smile and Slasher Smile stages. It's very, very much a bad thing for Haruko to be entertained.
Mahou Sensei Negima!! plays this for comedy; if Haruna starts smiling, something embarrassing and/or unpleasant is about to happen. The other characters are rightfully scared of her.
Invoked by Kaede when speaking with "Kunel Sanders", a mysterious, suspicious, and very powerful man who is interested in Negi but refuses to say why. In the end it turns out that he is trustworthy, but he also admits people tend to not believe his smiles.
Higurashi no Naku Koro ni has a few characters sport these. Most of the time it's either Mion, Shion, or Satako, and it usually involves getting Keiichi into a ridiculous outfit, pulling a prank, pushing someone's buttons or out of his clothes entirely.
Not to mention Ciel. When he fakes a smile, it's adorable. When he gives a real smile... It probably means someone is about to get hurt. Badly.
And in one of the OVAs? Grelle literally had the Cheshire's smile while playing the Cheshire Cat!
Bel from Katekyo Hitman Reborn! tends to have this as his default face, along with making one when he laughs his creepy "Ushishishishi~" laugh.
Hmmmm... notice how his default outfit is actually a pink and purple striped shirt? And how in one Omake he's considered a house pet in the Varia family? Looks like the resemblance isn't just the smile...
Naruto Uzumaki smiles like this a few times, usually when thinking of a prank. Some of those times (notably in the 101 episode) his Cheshire Cat Grin overlaps with Slasher Smile.
The Kyuubi's face is eternally twisted into a Cheshire Cat Grin.
XerxesBreak from Pandora Hearts has a very typical one. And his doll has exactly the same smile. And, oddly enough, the character called the Cheshire Cat does not.
Lots of the eponymous Titans of Attack on Titan sport unnerving grins, even when they logically should be in pain. For some these cross the boundary into Glasgow Grin because of the fact they're missing bits of skin.
Roronoa Zoro from One Piece, whenever he's not sleeping or eating. Also, Urouge.
Ham Egg from Osamu Tezuka's works is easily indentified for making this grin constantly, which foreshadows his unpleasant and villainous nature.
Fullmetal Alchemist: Truth's grins are the only visible feature on his otherwise blank body and are too wide and large to be physically possible on a human being. The fact that he lacks eyes or eyebrows makes identifying the emotion behind the grin impossible.
The Gold-Tooth Alchemist echoed this, often wearing a bizarrely-wide grin at times when there was no discernible reason for anyone to be smiling. Add the unfocused eyes and it moves into Slasher Smile territory.
Neon Genesis Evangelion: Asuka pulled one off in her debut episode when Gaghiel attacked the UN fleet carrying her Eva.
Shinji: This is really bad! We've got to go back and find Misato! Asuka:(looks sideways and grins) Wunderbär!
Kaworu often wears one himself, particularly in the manga or any of the other alternate universes where he pops up. It fits in well with his cryptic nature.
Totoro himself smiles like this when he is happy or delighted by something.
Films — Live-Action
The Machinist: Ivan does a particularly disturbing rendition of this trope.
Pirates of the Caribbean: Right before taking vicious or manipulative action, Captain Jack Sparrow often sports an evil, toothy smile. In the screenplay for Dead Man's Chest, a "Cheshire grin" is mentioned in Jack's direction during a particularly loathsome act of betrayal.
The allegedly-catatonic Cameron, just pulled up from the bottom of a pool after keeling over into it face first, broke into one of these in Ferris Buellers Day Off when Ferris and Sloane realize he saw Sloane stark naked while she was changing into her swimsuit, and enjoyed every minute of it. Cameron's ensuing hysterical laughter led to further dunkings by Ferris.
Dr. Frank-N-Furter walks on stage with this expression in the Rocky Horror Picture Show, and it's his default expression when he's not angry, jealous, megalomanical, or begging for sympathy. No real surprise really, as Cheshire Cat is actually a nickname for the actor Tim Curry.
Similarly in his role in Home Alone 2: Lost In New York. They even segue quite unnervingly from his grin to a still from the animated version of the Grinch — the resemblance is uncanny.
Equilibrium's Cleric Brandt has a smile which first inspires Fridge Logic when you realise that he's not supposed to have any emotion, then Fridge Brilliance when you realise that he doesn't have any emotion; his huge smile has nothing to do with real happiness or real satisfaction. Knowing this makes it pretty creepy.
Zero Mostel as Pseudolus delivers one of these to Jack Gilford's Hysterium in A Funny Thing Happened on the Way to the Forum. They've determined that the only way to get a visiting Captain to leave is to convince him that his intended bride is deceased. Hysterium intones, "But where are we going to get a body?" whereupon Pseudolus does a slow take at him with a grin that almost breaks his own face.
Cap:*having just told everyone else what to do, in detail, looks to Hulk* Hulk? Hulk:*looks down at him* Cap:*points up at the Chitauri invaders* Smash. Hulk: >:D
The movie version of How the Grinch Stole Christmas! also has the scene where the Grinch grins at his "wonderful, awful idea", except also the Slasher Smile one is done in an extremely nasty way during the "You're A Mean One Mr Grinch" musical number, the "You have termites in your smile" line and we are treated to a closeup of his mouth and we see his teeth which have bugs crawling around in them.
The Trope Namer is the Cheshire Cat◊, from Alice's Adventures in Wonderland. He's a mischevious creature, but not malicious to Alice or anyone who doesn't seem to deserve it. He even manages to mock the Queen of Hearts and then fade away before she can retaliate. The character is a play on the phrase "grinning like a Cheshire cat," which simply means smiling broadly. No one is exactly sure where the phrase came from.
Angua in Feet of Clay gives a rioter "a friendly smile. That was to say, her mouth was turned up at the corners and all her teeth were visible."
From Wyrd Sisters: "Greebo's grin gradually faded, until there was nothing left but the cat. This was nearly as spooky as the other way round." Keeping in mind that this is a housecat who rapes wolves and terrifies bears.
"It was a smile like the one you find on black and orange striped creatures prowling through the jungle looking for someone to smile at."
Similarly, Vimes is once noted to have a grin like the one pointed at swimmers and has a fin on top.
Ford Prefect from The Hitchhiker's Guide to the Galaxy is said to smile in this way, "a little too broadly, giving people the unnerving impression he was about to go for their neck."
Artemis Fowl has Artemis' signature vampire smile. It's just as creepy as it sounds.
Marunde in Someone Else's War wears one of these, though the narrator calls it a "crocodile grin."
Treecats in Honor Harrington can apparently pull this off masterfully. Given their propensity for mischief, it's highly appropriate.
Capt. Jacquelyn Harmon: I've always figured Carroll must have met a treecat in an opium dream or something when he invented the Cheshire Cat.
The Weasly twins in Harry Potter are noted to do this when they see a new target for mischief, even worse since they do it at the same time.
Dr. Phlox in Star Trek: Enterprise does this in the pilot. Season 4 reveals that his species are capable of inflating their heads, which goes some way to explain why Denobulan smiles don't lead to self-decapitation.
Not quite a Cheshire Cat Grin, but with the same effect in "Bride of Chaotica!" an episode of Star Trek: Voyager. The holodeck malfunctions, and someone must go into the program to resolve the issue playing the part of Queen Arachnia. When Captain Janeway asks Tom "Who do you have in mind?" Tom, and the rest of the crew turn to her with evil smirks.
Talk show host/Comedian Jay Leno always seems to have one of these on his face.
Theo Kojak pulls out one of these at least every couple of episodes.
Television Without Pityrecap: I think part of the actual — not the endlessly explicit and told-not-shown, but the actual, the perceivable — charm of River is her lovely smile when she's doing something really awful.
Strangely enough, the gentle, unassuming, adorkable Fifth Doctor often wore one of these, especially when talking to people taking him prisoner. He smiled most of the time, in fact, but it very rarely reached his eyes.
In the Eighth Doctor Adventures novels, Fitz has been known to smile "with a wicked twist to his mouth that showed far too many teeth", although he's really a very Nice Guy under the somewhat sleazy exterior and it doesn't tend to mean he's really up to anything all that bad.
Jon: (in Fourth Doctor voice, pulling goggle-eyed, grinning face) Now, with Tom Bakerrr you get one kind of eyes and teeth... and (in Tenth Doctor voice, pulling a massively different goggle-eyed, grinning face) with you, ya get anather kind af eyes and teeth.
Vala in Stargate SG-1 has a grin that shows a lot of teeth and can be deeply disconcerting.
Michael Westen from Burn Notice does this a lot. His smile will eat your soul.
Nikola Tesla (as played by Jonathon Young) on Sanctuary.
Kamen Rider Fourze has stoic "I don't wanna be involved with this Kamen Rider Club" foolishness Kengo Utahoshi have one of these as he drags the poor Butt Monkey JK into piloting a mecha known as the Power Dizer.
Justified has Detroit mob lieutenant Robert Quarles, who has a big, unsettling smile.
Babylon 5: Mr. Morden will give you a big jovial-looking smile, just as he's about to screw you and your entire species over.
Sister Julienne of Call the Midwife, nun-in-charge of Nonnatus House, has one, which she usually deploys right after she has "asked" someone to do something. The "or else" is implied.
Smallville: Tess Mercer's smile is always a sign she's plotting something. Somewhat subverted, in that she does ave a genuine smile she can use when happy, and her intentions are always for the greater good, but when plotting, her smile can be downright scary.
In thisGarfield comic strip, Garfield tormented Jon by Cheshire cat grinning in the dark.
Another strip had him entering a room where Jon was with a huge, toothy smile and shifty eyes for no apparent reason. Jon, annoyed, asked: "All right, Garfield - what have you done?" Garfield of course remained silent, prompting Jon to keep demanding what he had done until he finally snaps and starts screaming: "WHAT HAVE YOU DONE?! WHAT HAVE YOU DONE?!" (Garfield hasn't done anything.)
Garfield: I love mental games.
One Beetle Bailey Sunday strip had Beetle torment Sarge by periodically giving him one of these smiles. Sarge tore his living quarters and office apart trying to find whatever Practical Joke Beetle had set up (in fact, there wasn't one).
In one Calvin and Hobbes arc, when Calvin notices Susie left her dolls outside while she had lunch, Calvin makes one and says "That gives me a brilliant idea!"
Very literal example in one series of Peanuts strips. Snoopy is listening to Linus read the chapter of Alice's Adventures in Wonderland where Alice meets the Cat, and then Snoopy grins widely. Linus is shocked when Snoopy disappears, leaving only his grin. Then he reappears, and says, "I've been able to do that for years!"
Done superbly in the David Tennant version of Hamlet. "O villain! Smiling, damned villain...", saying this all while sporting a spine-chilling smile. We know his sanity is long, long gone.
In the Super Famicom title Monopoly 2, there are four tournament players in each match including the player. Two of these opponents (which include fortune tellers, ventriloquists, and salarymen) are dupes, and one is a smug snake par excellance. Want to know which? Just keep your eye out for this facial expression.
We also have Sableye◊ from Gen III, but it's generally hard to smile pleasantly when you have a mouthful of sharp teeth.
Tohsaka in Fate/stay night is described as being scariest when she's smiling, because then you know she is going to get you. Nobody else is ever happy when she smiles.
That's nothing. Sakura's can silence a room and extinguish candles. It makes sense. They are sisters, after all.
Mario & Luigi: Fawful's face seems to be permanently frozen into this expression. Whether he's dropping a giant rock on our heroes, fighting them off in a mech, selling them badges, or mutated by the power of a Sealed Evil in a Can into a freaky bug thing, he always has a giant toothy grin on his face.
Super Paper Mario: Good ol' Dimentio's mask/face is always curled up into an unnerving smirk. Although, to be fair, he was never even trying to be on the heroes' side to begin with, so no mystery there. Beyond that, it was more so when he ended up possessing the final boss, though that arguably made his joyful look even more unsettling.
Taokaka of BlazBlue typically makes this face whenever she wants to "play" or she's about to attack some poor fool. This being a game that centers on, y'know, fighting, she keeps the expression some 90% of the time.
Travis Touchdown of No More Heroes, particularly whenever he enters a fight while in a good mood. The loading screen for the second game even shows a small picture of him sporting one.
The Judge in OFF sports a permanent one. Ironically, he's probably the nicest character in the entire game. Even better, he's actually a cat.
Touhou characters have such a warm and cheerful smile, even when speaking grim or gory things. But have you seen some art made by fans with Flandre? Yuuka? Marisa? Reimu? Yukari?
This is pretty much Jade Curtiss's default expression throughout Tales of the Abyss. He's more often seen as a Stepford Smiler since he's a borderline sociopath with Dark and Troubled Past, but he's also the game's king Troll, and when he's trolling "Cheshire Cat Grin" seems a more appropriate term.
Whenever The Cheat from Homestar Runner smiles, it's this kind of smile. Things often backfire on him, though.
Pinkie Pie in the Pony Video "We're Going for a Ride" gives off one of these, and turns it Up to Eleven by turning the entire screen dark and all you can see are her eyes and mouth!
Pinkie Pie: Lock the doors and close the blinds, we're going for a ride!
Both Zimmy and Coyote in Gunnerkrigg Court. Oddly, the effect of each character's grin is heightened by the fact that they have the wrong sort of teeth: Zimmy has shark-like teeth and Coyote has uniform, flat teeth.
Of course, both of them pale before the awesomeness of Jack's smile.
In Girl Genius, "wild" Jagers tend to wear this most of the time: there's so much funny things to happen — like plowing through a crowd of monsters — and they have pointed teeth. Gil grins like that when he is stuffed to the gills with combat stimulants and about to blow up something.
Sparks tend to wear a huge grin when they've got an idea. Considering the stuff they usually invent, this is seldom good news for anyone in town.
Dagre from The Meek sports one...kind of. It's more of his jowls drooping, giving an absolutely terrifying grin appearance.
Subverted/defied with Florence Ambrose in Freefall — her natural smile is a face full of teeth, since she's an anthropomorphic "Bowman's Wolf." She has to remember to smile with her lips closed to avoid this trope — though she's not above invoking it...
Occasionally, Sam gets one of these. That's rather a lot of teeth for an squid in a suit...
Several tricksters and fair folk do this in Roommates but the grand master is the Scribble Person/Living Words ( aka the vaguely anthropomorphic personification of the Story) whose hard-to-trust grins can literally spell things like "Sacrifice" or "Tragedy" especially when (s)he is offering deals.
In Ruby Quest, Red has one of these for half his appearances. Ruby keeps just managing to miss it when they get particularly freaky.
In the penultimate episode of Teen Titans, a character named Cheshire appears, wearing a large mask with a permanent Cheshire Cat Grin on it. One of her powers was to turn invisible except for the eyes and the grin, much like the cat in Alice in Wonderland.
She's in the comics, too, minus that power. For the record, her name is Jade Nguyen, and she has done things justifying that grin (like nuking Qurac).
The Amazing Mumbo gives off a rather literal example in "Bunny Ravennote (Or How To Make A Titanimal Disappear)" .
Mumbo: Tonight, I will make the Titans disappear... (Dramatic Pause) ...forever.
In Young Justice, Jade has the mask (which isn't in the comics. The previous animated Cheshire made just that much of an impression in her less than a minute of screentime.) but not the invisibility. She's an assassin for the League of Shadows initially, but is far from Ax-Crazy enough to nuke a small country out of existence For the Evulz. She also has more than one mask (since one of them currently resides in Kid Flash's trophy case.)
On The Grim Adventures of Billy & Mandy, shapeshifter Nergal Junor replaces the teacher in order to get revenge on the class bully Sperg. "Ms. Butterbean" approaches the bully with a smile that starts as a Psychotic Smirk and quicky grows in width, as well as tooth size and sharpness, until it's grinning fanged maw as wide her head.
Timmy gets one of these himself, in the episode F.L.A.R.G. Mark sums it up pretty well.
Mark: What's with the face? It is happy, yet at the same time, disturbing!
In the Code Lyoko episode "Killer Music", Odd has one of these planted on his face for all but a few minutes of the episode... while comatose and dying.
In the Exo Squad episode "A Traitor Among Us", J.T. gets one of these when he explains his plan for getting The Squad to Venus. "We need to become official undesirables. That's one assignment you troopers might enjoy."
Henry and June (the latter more often) do this in KaBlam!!
Twilight Sparkle of My Little Pony: Friendship Is Magic pulls one off in "Lesson Zero" when she prepares to create an argument amongst the Cutie Mark Crusaders in a bid to solve the said problem and have a friendship report to write to Princess Celestia.
T-Bone from SWAT Kats donned this grin occasionally, almost uniquely amongst the characters of that series.
More often than not, Mr. Bogus will very often grin like this whether the situation calls for it or not.
Chimpanzees "smile" by baring their teeth as a way of warning potential challengers that this chimp is not to be messed with. This has led to more than a few people getting mauled, because, hey, the monkey is smiling at 'em! And ain't he just like a little person? Maybe he wants a hug! NO. When a chimp smiles at you, he's telling you to fuck off. By the way, those teeth? They go for the face. And chimps are strong. Mister Peanutpants does not want to be your friend, kids.
In fact, this is true of many animals, since their teeth are their main weapons. Its meaning is lost for humans because of our greater variety of expressions and because our teeth are puny compared to theirs.
Former Australian Treasurer Peter Costello was famous for his Parliamentary savaging of his opponents in debate, of which his Cheshire Cat grin would be a prime indicator to get out of the way of his victims.
Tony Blair was known as the Cheshire cat (then the less favourable "Cheshire twat") since he became leader of the opposition and then prime minister due to his smile.