Dissonant Laughter

There are some characters who fight for glory, or to atone for their past deeds. Some of them don't really want to survive. Then you've got all the heroic motives - Greater Good, for friends, for society, the list goes on.

And then you've got this guy.

He'll be right in the thick of the battle, laughing his head off, and genuinely enjoying himself. Whatever the reason, he's simply enjoying the fight. This can be downright creepy.

Like the character who displays Dissonant Serenity, the one who pulls off Dissonant Laughter is very definitely at odds with the world around him, although, rather than contrasting chaos with calm, they will contrast the grim battle with their lightheartedness.

The nature of the laugh is not important, either - it can be maniacal, like the Laughing Mad, a mildly psychotic chuckle, whatever the character feels like at the time - so long as it's because they're having the time of their lives.

Compare Dissonant Serenity and Laughing Mad. Can be a characteristic of the Blood Knight. Contrast Berserker Tears.

Examples of Dissonant Laughter include:

Anime and Manga

There's a lot of this in Baccano!!, mostly on the parts of Ladd Russo and his buddies. The most dissonant example comes from Dune, who giggles maniacally as Claire Stanfield dangles him off the caboose of a moving train and grinds his arm to bits against the tracks.
Some of the Extendeds in Gundam SEED and Gundam SEED Destiny.
Donquixote Doflamingo of One Piece definitely fits the bill here, as he is pretty much always seen laughing, or at least grinning widely, even as he forces people to fight each other to the death, among other things. This is cranked up even further during the war with Whitebeard, where he reacts to pretty much everything with psychotic laughter, cementing his role as an Ax Crazy.
Soul Eater's Franken Stein gets like this at his craziest, notably when facing Medusa, and it's pretty alarming. Even when not at his craziest, he sometimes sports a wide grin while beating the crap out of people. And he's a good guy... on most occasions.
Bleach has consummate Blood Knight Zaraki Kenpachi.
Kemonozume has Ooba who is obviously completely insane but is obviously enjoying himself immensely and is often seen chuckling or laughing like a maniac.
Whenever Shion is the "crazy one" she's prone to this. After she kills Satoko, shortly before remembering Satoshi asking her to protect his little sister, she snaps and is laughing even harder. Even while falling off the roof of a building.
Tsuruya of Suzumiya Haruhi is The Hyena and has laughed, serious or not, for everything, practically.
Scorpio Kardia in Saint Seiya: The Lost Canvas. His opponent Wyvern Rhadamanthys is not amused.
Shin Kazama does this in the last issue of the Area 88 manga. After witnessing the deaths of Saki, Mickey, and Sela, Shin is so emotionally overwhelmed that he starts laughing hysterically. His laughter makes Kim extremely uncomfortable. He returns to his senses when Kanzaki contacts him.
In Puella Magi Madoka Magica, Sayaka Miki begins to laugh and smile during her battles as a result of her effectively becoming a Death Seeker as she lets her Soul Gem darken. She also giggles insanely during one of her special attacks in the PSP game.

Comics

The Joker. In The Dark Knight, a cop and Batman separately beat the crap out of him (for different reasons); not only doesn't he fight back, but he's also cackling like a hyena the entire time.
- Also, Batman in All Star Batman and Robin was laughing like a maniac while driving through a bunch of cops.

Live Action TV

Guido Geller from Camera Cafe is known for his downright moronic laughter (hee-hee), usually when he talks about either old oriental legends, firing someone, or the smell of a fried hamster.
The usually straightlaced Adam Adamant tends to chuckle maniacally when fighting mooks, especially if he's been played in the episode; needless to say, it really creeps his opponents out.
The Sherlock version of Sherlock Holmes isn't one for laughter, but you don't see him happier than when he's on a case.

John Watson: Enjoying yourself? ... I'd drop the smile. Kidnapped kids, remember?

Film

Baby Face Nelson, from the new movie Public Enemies, has to be dragged into the car to stop him laughing and killing people.
- A character in O Brother, Where Art Thou? laughs while firing a tommygun. He stops laughing when someone calls him 'Baby Face'. The character is of course George "Babyface" Nelson. Later after gleefully and manaically robbing a bank, he becomes depressed and wanders off, trailing sad dollar bills behind him.
  - The Real Life Baby Face almost certainly suffered from bipolar disorder (manic depression).
Tyler Durden laughs like a maniac while Lou beats the snot out of him. Then for poor Lou, It Gets Worse.
In the film adaptation of The Two Towers, Gandalf laughs heartily during his Big Damn Heroes moment as he casually beats the terrified Uruk-Hai with his staff. It was glorious.
Funnily enough, The Joker. Throw him off a building, and he'll laugh like a Disney villain.
- Won't die like one, though.

Literature

Mike Hammer was this way during WW 2, as related in One Lonely Night.

"You should have seen the way they looked at me; you'd have thought I'd had fangs."

Sirius Black does this all the time. Notably, when the wizard police find him in a street full of corpses, and later on when he's being killed.
Ford Prefect laughs while the earth is being ripped to shreds for the last time.
In The Belgariad, Mandorallen begins to suffer from phobophobia after he experiences fear for the first time. He's advised that it's normal for brave men to be frightened once in a while, and that he should laugh at his fear to alleviate it. He takes this literally, and makes a habit of laughing out loud while charging into combat, which irritates his companions considerably.
In The Dresden Files, Harry's psycho fairy godmother, Lea, likes killing. Really, really likes it.
- Sanya is also described as laughing while in combat, though in his case it may be more of an adrenaline issue than Lea's bloodlust. Or maybe he just really likes smiting evil.
Ganner Rhysode, a wayward Jedi in the New Jedi Order series, struggled his entire life with his need to be the hero. After being captured by the Yuuzhan Vong and rescued by Jacen Solo, he realizes that playing the hero had always been his greatest weakness, but it could also be his greatest strength. He uses the knowledge of who he truly is to become one with the Force and rushes out to hold off the Yuuzhan Vong warriors, buying Jacen the time he needs to enact his plan. After his badass one-liner of "None shall pass," Ganner fights and slaughters hordes of Vong warriors...laughing delightedly the whole time.

Theatre

In Ajax, the protracted torture of sheep is upsetting enough for Ajax's friends and family, but the sheer glee Ajax derives in doing so (thinking he is torturing Odysseus) just makes it worse.
In the stage play of Les Misérables, it's common to have Thenardier let off some cackles during the "Dog Eats Dog" number. Considering that he's gleefully looting the bodies of murdered men, and singing about how the world is a sack of crap, he definitely counts.

Video Games

Deconstructed with Laughing Octopus in Metal Gear Solid 4. True, she cackles madly during her battle with Snake, but it is revealed that she was captured by enemy soldiers and forced to laugh as she killed people. This drove her insane, and it is implied that she continues laughing to keep from screaming or crying.
In Condemned 2 the boss character of the Doll Factory tends to get giggle fits related to this.
Space Channel 5 Part 2 has Purge. It doesn't help that in the Japanese version of the game, he's mentally ill to the point of being a Psychopathic Manchild along with being a Dark Messiah.

Web Comics

Jagermonsters, of Girl Genius fame, tend to go into battle with a joyful demeanour. Then again, they're just so damn goofy that it's hard to think of them as creepy or frightening.
Lackadaisy's Freckle does this whenever he gets ahold of a gun. He enjoys shooting people perhaps a bit too much. This is actually why he was rejected from the police.

Web Original

A frickin' disturbing example (which used to be the page image) comes courtesy of Red from Ruby Quest during this scene. He has just pulled down the tarp in the room Ruby woke up in the second time, revealing a stitched-up, bloody body pinned to the wall.
Veronica Carter is always doing this. During the final battle, when she was singlehandedly dueling Valentine in the middle of an Anyone Can Die final battle. She was laughing like a child at an amusement park.

Western Animation

Blitzwing in his Random persona of Transformers Animated will laugh at everything no matter what, but he is especially giggly in battle.
In Happy Tree Friends, Nutty laughs all the time. Sometimes he even laughs as he dies.

Real Life

At Lizzie Borden's double-murder trial, one of the pieces of evidence against her was the maid testifying that, during the interval between Lizzie's stepmother being killed and Lizzie's father coming home and being killed, she had heard Lizzie laughing at the top of a staircase. It should be noted that a person standing at the top of the staircase would have been able to see into the second floor room and look at the step-mother's body.
Tennessee Williams, no tower of strength when it came to Adaptation Decay (In a toss-up, Elia Kazan chose lightning-charged energy over subtlety every time), got his revenge when the film of A Streetcar Named Desire came out. While the rest of the audience would be barking like seals at Blanche Dubois being committed, Williams was wooping it up in the back row. "Now she's off to the bughouse!"