The literary example, Gwynplaine of The Man Who Laughs by Victor Hugo, which is commonly cited as inspiration for The Joker, involves a man whose face is horribly mutilated so that he cannot stop smiling and how his psyche is twisted by this. In order to maintain the grin throughout the movie, actor Conrad Veidt had to get metal hooks in his mouth to pull back his cheeks. Nevertheless, the character is a really nice guy. According to Bob Kane and Jerry Robinson, Bill Finger produced this photo◊ of Veidt while developing the character.
In Frank Miller's All-Star Batman & Robin, the Boy Wonder, the Dark Knight himself has one in both his costumed and civilian identity, especially when thinking about his young ward. In one scene, Batman even laughs in excitement, with the narration saying how he haven't slept in days yet is full of energy.
Batman: The Black Mirror: Dick Grayson busts one out a couple of times when he wants to rub it in a criminal's face.
The magically created Batzarro is the opposite of Batman in every way he can be — so since Batman is grim and serious, Batzarro has a wild, fanged smile (and no eyes, making his smile freakier).
Coming from the Dark Multiverse introduced in Dark Nights: Metal, there's the Batman Who Laughs, a nghtmarish version of Batman born out of him getting infected with a Joker Gas that turned him into a jokerized Batman. The Batman Who Laughs is insane, wishing to corrupt and destroy every reality possible, all while laughing with a distorted smile of his. In his own words, "in order to win, you need to adapt, and to adapt, you need to laugh away all restraints.[...] A Batman who laughs... is a Batman who always wins."
Laughs design has been noted to resemble and being inspired by Judge Death, from Judge Dredd. A 2019 story written by Rob Williams does a Shout-Out to the DC character with the title "The Judge that laughs".
Bullseye.◊ Yeah, you see that space where he's missing a tooth? That's cause he killed a guy with it.
Crossed: This seems to be the default expression of the Crossed.
In the DuckTales comics, Magica's Launchpad clone makes a very evil grin as he pulls a gun on Scrooge.
Evil Ernie tends to have a huge friggin' grin while engaging in murder. This extends to his maybe-sentient friend Smiley The Psychotic Button. Lady Death is also often shown sporting a slasher smile when encouraging Ernie to kill for her.
Subverted in an issue of G.I. Joe. Formerly masked gunmen hold a family hostage in a remote house with the result being the authorities are not sure at first who are the hostages and who are the hostage-takers. One of them seems to be grinning maliciously all the time and the footage they have of the masked rampage shows them all grinning like maniacs while gunning down innocent people. So obviously the one with the constant grin is one of the bad guys? Wrong, he's the father of the innocent family caught in the middle, and a veteran who had suffered permanent damage to his facial muscles during active military service.
Grimjack sports one whenever he is in a fight. The smile is an involuntary tick that he developed as a child gladiator where he was known as "The Grinner." Also, combat is the only time you ever see him smiling.
Infinite Crisis: The last image of the book is Superboy-Prime grinning after carving a haphazard Superman logo on his bare chest.
Johnny of Johnny the Homicidal Maniac would usually have one while torturing or killing victims. Mr. Eff and Psychodoughboy had permanent ones because Johnny painted them onto their faces.
Judge Dredd: Dredd's undead arch-enemy Judge Death does this all the time as well, sporting a big toothy grin. Mostly because his lips have rotted off, but even more attention is drawn to it because similarly to Dredd, his helmet conceals the rest of his face. While hardly hilarious, out of all the Dark Judges, he's naturally the most prone to Faux Affably Evil behavior.
The Mighty Thor's enemy Malekith the Accursed looks like the offspring of Drizzt Do'Urden and Two-Face, with a smile like the Joker.
Kid Miracleman from the series of the same name is constantly depicted with this facial expression. The scariest example is probably from the cover of Issue #15 (which can be found in the Image Links) — truly horrifying just from the sheer inhumanity of that grin.
Pinkie Pie does a face like this in page 9 of Issue 1 of complete with a "cut/slit throat" gesture.
Cosmos, the Big Bad of issues 75-78, loves doing this. She strikes a particularly menacing one after finally realizing that Discord really has changed, when she replies "I haven't".
Primal Warrior Draco Azul: In the second issue, when attacked by a group of thugs Eric Martinez picks up a knife and grabs one of them by the throat with a bloodthirsty grin, before relenting due to Ramona Escobar watching.
The Corinthian has three: he has devouring mouths instead of eyes behind his shades. Fitting, since he's the eidolon (the word eidolon being especially apt here: it connects strongly to concepts such as delusion, idol, spirit, or bogeyman) or archetype dream that inspires and is inspired by Serial Killers.
The Green Goblin is usually portrayed with having this in the comics and most adaptations. On his human face and his mask.
In fact, symbiotes appear to have some sort of demonic smile on their faces sometimes.
In the classic Spider-Man vs. Wolverine, there's a scene where they're duking it out in an East German graveyard. Spider-Man thinks, "I'm hitting him hard enough to wreck cars... and I can't get him to stop smiling..."
In Bizarrogirl, an human-like android created by villain Dollmaker displays a psychotic grin while abducting a child.
In Who is Superwoman?, Reactron sports a wide and absolutely insane grin when he's going to murder his ex-girlfriend. And when he's attempting to murder Supergirl. Generally, he always smiles when he's looking to kill someone.
The Hunt for Reactron: After being chastised by commander Perseus Hazard, Reactron grins widely behind his back, a hint that Reactron was already planning to kill him.
In Super Sons, Damian Wayne flashes one as he informs Lex Luthor about eleven explosives he left around his lab (which were really just fakes to throw him off).
In The Unknown Supergirl, Lesla-Lar impersonates Supergirl, and after convincing a totally clueless Superman that she is ready to go public, she grins widely as pondering her future plans to get rid of Superman and Luthor before conquering Earth (or destroying the planet if it pleases her).
In Superman vs. Shazam!, Karmang grins wickedly while visualizing the kind of planet-wide destruction which will happen if someone tries to dismantle his world-ending engines before they activate.
While Cyclonus is one of the good guys of The Transformers: More than Meets the Eye, his preferred brand of smile is less "I am happy that the world is a nice place" and more "I am happy that the world is going to be a nicer place when I finish cutting you out of it." He does occasionally get the other sort, though.
Very often shown by Spider Jerusalem from Transmetropolitan. The Presidential candidate known as "The Smiler" also has that name for a very good reason.
Twisted Dark: The comics make liberal use of this trope, sometimes in the story's Twist Ending, such as when the police officer in "Drink Driving" who's putting Mrs. Conatser in his car puts one of these on when he says he's not a cop.
One of the last things you want to see is Hawkeye covered in the blood of the squad you sent to subdue him, holding their weapons and grinning into your security camera telling you, "Run", when you are part of the group responsible for his family's murder. Unfortunately for you, it is the one of the last things you're going to see.
Captain America gave one to Herr Kleiser when he informed him that his mission was to blow up the train they were in, and not capture it as he thought.
Ultimate Galactus Trilogy: Carol Danvers looks way too enthusiastic about handing Marh over to the scientists for an old fashioned vivisection.
The Juggernaut enjoys his role as an unstoppable engine of destruction. This is especially apparent when Rob Liefeld drew him.
Mystique in the Wolverine story arc "Get Mystique"; just before their final climactic confrontation she strips naked, festoons herself with weapons, puts on a slasher smile and says, "Come and GET me, Lover!"
X-23: Kimura whenever she's hurting or killing something. When she stomps on a little girl's skull with her boot, all we see is her grinning face. In one case she wears it while carving X-23 up with a chainsaw.
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