This is a subtrope of Evil Laugh, and the opposite of Dissonant Serenity. It's when a character goes around killing everything in sight and seems to be having a lot of fun with it, like Joker levels of fun. Especially if the character is Laughing Mad.
Typical of the Blood Knight, the Boisterous Bruiser, some Ax-Crazy characters, some Glory Hound military officers, and some Sociopathic Heroes, but it can happen to anyone, especially during a Heroic BSoD, a Heroic Sacrifice or a Bolivian Army Ending. It's rather exceptional for normal heroes, since usually there's something deeply wrong if The Cape is actually having fun killing people (unless they're trained to do so).
If they actually say the title phrase, they're engaging in You Put the "X" in "XY".
In a possible aversion, the 80s/90s rock band Slaughter used this as an explanation of their name.
- Dragon Ball Z
- Kid Buu for the most part can be summed up as "Destroy, destroy, destroy and laugh, laugh and laugh some more."
- There's also Freeza laughing at the destruction of Planet Vegeta.
- Many lesser mooks in Fist of the North Star, especially the Fang Clan, outright enjoy robbing and slaughtering the poor, and it's quite common for everyone of them to laugh while gutting their unfortunate victims.
- Zentraedi leader Boddole Zer in Super Dimension Fortress Macross gives a hearty "Muahahahahahaha!" as his fleet is destroying the Earth's surface and killing billions of humans.
- Hidan from Naruto.
- Roberto tended to do this in Monster while Johan was more... calm about it.
- While the anime version of Elfen Lied portrays Lucy as The Stoic Emotionless Girl who butchers people like the dozen without visible emotion, her manga counterpart displays a disturbing tendency to break in fits of insane cackling as she ripped people to pieces with gleeful abandon.
- It wasn't manslaughter, but the end of the great fight between "Nagi" and Rakan in Mahou Sensei Negima! shares the spirit.
- Mad Pierrot from Cowboy Bebop. To Nightmare Fuelish levels...
- Kenpachi Zaraki is kind of the embodiment of this trope, although we only see him doing duels.
- Several characters in Hellsing (though most often Alucard) engage in this.
- Yuno Gasai from Future Diary engages in this.
- Typical of the Go Nagai style brand of Super Robot Genre show, especially Mazinger Z.
- In Devilman, everyone does this at one point or another, but the titular Type IV anti-hero takes the cake. A cake made of brutality and guts.
- In Berserk, many people take sick amusement in killing, especially Apostles such as the Baron of Koka Castle who laughs maniacally while massacring innocent townspeople.
- Guts as a rage-filled Anti-Hero has laughed while slaughtering all around him in at least one of his darkest moments. In the Lost Children chapter while being attacked at night by the flaming ghosts of dozens of children who he had killed earlier when they were possessed monsters, he laughs with wild abandon as if taking sadistic joy in cutting them down. However, his subtle reactions betray the fact that he's using this frenzied state as a coping mechanism to keep fighting through the nauseating guilt and horror that he's feeling, and he immediately snaps out of it when he sees Jill in the midst of the danger and shields her with his own body.
- Accelerator of A Certain Magical Index laughs insanely during every single one of his fights, most of which involve lots of killing.
- Higurashi: When They Cry: Shion Sonozaki, during Meazaki-hen and thus Watanagashi-hen. There are pictures of her face with "You can't spell slaughter without laughter" captioned to them around on the internet, and she's pretty much the literal poster child for this trope.
- Though she didn't laugh when she actually killed, Rena does go Laughing Mad while trying her best to kill Keiichi and Rika. Images of her wielding her hatchet with an open-mouthed roaring laugh are iconic.
- The Gundam franchise's three big Psychos For Hire, Yazan Gable, Ali Al-Saachez, and Desil Galette are all guilty of this, chuckling to themselves as they gun down MS after MS. Gundam SEED and Gundam SEED Destiny's Extended are not better about this, nor are their creators, Muruta Azrael and Lord Djibril.
- Dinoponera from Arachnid. One moment she's an affection-needy cutie pie; the next she's maniacally beating her friendship candidates to a bloody pulp.
- Rory Mercury from Gate laughs with glee as she fulfills her obligations as the Apostle to Emloy, the god of death.
- The Joker in most of his incarnations, except when he's taking killing seriously.
- As demonstrated in the former page picture, in The Dark Knight, he actually rides a circus truck emblazoned with "laughter is the best medicine", and a large red S spray-painted just before "laughter".
- Spider-Man foe Carnage also takes great joy in killing, as his name oh-so-subtley suggests.
- Bullseye is this to a T. His sometimes friend/sometimes enemy Deadpool is also a good example.
- Shakara: The Overlord laughs maniacally while massacring all of his former allies in The Hierarchy after they discover his betrayal.
- Pinkie Pie in the infamous My Little Pony: Friendship Is Magic fanfic Cupcakes, who giggles at doing horrible things to her victims.
- This has led to the fans realizing that Pinkie, as the Element of Laughter, really DOES put the "laughter" in "slaughter".
- Some Frozen fans decided to create a fan-made Villain Song "Let Them Run", set to the melody of "Let It Go" in which Anna giggles as she sings about murdering people (including her sister Elsa) like it's as fun as building snowmen.
- Hot Shots! Part Deux is the most violent movie ever made! And it has a lot of fun proving that.
- Jack Nicholson at the climax of The Shining was partly this.
- Corrupt Corporate Executive Max Zorin in A View to a Kill likes gunning down his own henchmen way, way too much.
- In Christopher Nolan's The Dark Knight, in the car chase on Wacker Drive, the Joker and his men are in a semi truck that has the slogan "Laughter is the best medicine". An S has been spraypainted to make the message say "Slaughter is the best medicine."
- In most of his appearances, King Ghidorah from the Godzilla makes an oddly discordant trilling/cackling noise instead of traditional roars; as he is described as slaughtering entire worlds for fun, it almost sounds like maniacal laughter.
- In The Sabata Trilogy, Carrincha and Escudo (two characters in two different movies played by the same actor) are this.
- Lord of War: During the weapons sale in Sierra Leone, Andre Baptiste Jr. is trying out the M60 from the first Rambo movie which Yuri finally brought him. He guns down civilians on the side of the road while laughing with glee.
- A rare heroic example in Drax the Destroyer of Guardians of the Galaxy. What sets him apart is that his laugh is very genuine - it's upbeat, happy, and excited, as opposed to the regular bloodthristy, sadistic laughter that most examples of this trope show off.
- Home Alone: In both the first and second movie, there's a Gangster Film Within a Film (Angels with Filthy Souls and Angels With Filthier Souls) in which a 1930s mobster uses his Tommy Gun to gun down various people while he laughs psychotically.
- Bellatrix Lestrange from Harry Potter. An authentic Ax-Crazy if she had an ax instead of a wand.
- Odiana in Codex Alera is completely Ax-Crazy and really quite cheerful (and self-aware) about it. She usually expresses this by being inordinately cute and cheery while suggesting that they just kill everyone in about a 5-mile radius.
- Rachel from Animorphs is a rare heroic (well, sort of) example of this. Right before charging into her final battle, she leaves us with this little gem: "I felt...I felt exalted. It was my moment. This was my place and my time and my own perfection. I was no longer afraid. Weird. If I'd had a mouth I'd have smiled. <Well?> I said. No one moved. <Scared?> I asked. No answer. <You should be,> I said, almost laughing. I lunged..."
- Tulkas, the god of war in J. R. R. Tolkien's universe is a rare good example of this.
- Edward Dunn "Ned" Malone, the journalist in Arthur Conan Doyle's The Lost World (1912) when he shoots the ape-like creatures (called Doda by the Accala natives). However, he is the main hero of the book
- Borenson of The Runelords starts chuckling and gradually passes into outright laughter whenever he fights. While he takes pride in being a good soldier, he's by no means a murderous madman and has no idea why he laughs while he fights. But he takes advantage of the fact that it unnerves everyone else.
- Pace of Heretical Edge is apparently completely nuts and frequently laughs in combat. It's not actually Pace laughing. It's the `broken` Seosten Lies possessing her.
- In Heroes, Sylar has a good bit of fun being a psychotic serial killer.
- Doctor Who:
- The easiest way to describe the new series' version of the Master is "completely insane... and loving every second of it."
- River Song is a Sociopathic Hero version, as she takes great delight in shooting down the bad aliens.
- The Yozi Adorjan from Exalted is infamous for this; the only sound she can stand is her own laughter, she swoops around the Demon City slaying all she touches, and murder is something she finds particularly amusing. Those who take enough of her Charms will also eventually adopt this attitude.
- Kevin "Maddog" Cameron from Jagged Alliance is a psychotic hick who can be hired by the player. He's prone to ignoring player orders when wielding burst fire weapons and loves fighting multiple enemies at once, and when his Morale gets high enough, he starts to cackle in an insane manner while killing the Queen's men.
- Any FPS that is Duke Nukem-ish enough has this:
- The characters in Left 4 Dead have a cackling sound file that some players set to play whenever they fired their guns.
- Caleb from Blood also periodically laughs maniacally when there's lots of violence happening on the screen... Such as when he just threw a bundle of dynamite into a crowd of evil cultists (and/or innocent civilians).
- Shion during her torture of Satoko in Higurashi: When They Cry.
- Eva-Beatrice at a bare minimum during her murder of Rosa, in Umineko: When They Cry. So much so that once just wasn't enough. And actually, Beato herself quite a few times, although it was stated in red that this was not the case.
- Kinzo, when he makes his 1st twilight appearance in episode 4, chews the dining room and most of the diners.
- Luca Blight. His motto might as well be "You can't spell 'Slaughter' without 'Laughter'!"
- Kefka, people! Just one of the MANY things he has in common with The Joker.
- In a similar vein, we get Yuuki Terumi, who laughs in the Anti-Hero protagonist's face after murdering his adoptive mother, burning her house to the ground, and cutting his right arm off.
- In Team Fortress 2, the Heavy Weapons Guy is notable for this, especially towards the end of the "Meet the Heavy" video. The other characters, too, apply when dominating an opponent.
- You may now do this at-will using the Schadenfreude taunt to laugh at someone so that they see you mocking them in their kill-cam. Needless to say, it's a great way to show how much you're enjoying killing people, and an even better way to honk them off.
- Wallachia of Melty Blood laughs madly even as he chops his opponents to bits. Not that you see any blood, but that's the impression.
- Dimentio in Super Paper Mario does this after "killing" Mario, Peach, and Bowser.
- Dawn of War: Khorne Berserkers, Chaos Space Marines and Ork Big Meks all have laughing sounds when attacking. Aspiring Champions even have a fast-paced laugh when their morale is gone.
- In Borderlands, Brick, the Berserker, seems to have a lot of fun beating people into a pulp with his bare hands while in his Unstoppable Rage.
- In Sonic the Hedgehog (2006), Mephiles laughs like a lunatic after killing Sonic.
- In Mass Effect 3 multiplayer, krogan characters let out a good laugh after they kill enough enemies in a row with melee and go into blood rage. Also happens sometimes with Grunt, your Krogan squadmate from the second game, who really enjoys killing things.
- Onmyōji: Kurodōji is a powerful shikigami, but we do hope you can put up with the constant cackles he lets out as he chops up his foes.
- Akechi Mitsuhide from Sengoku Basara is Laughing Mad in the first place, but once you get him in the heat of battle, oh boy...
- The Warlock from Dota 2 is usually quite deadpan, but if he manages to scrounge up upgrades to his ultimate, he can summon up to four demons at once (as opposed to one normally), and starts to lose his cool and laugh maniacally.
Warlock: Can you believe this!? Ahahahahaha!
- Miss Fortune from League of Legends will laugh maniacally when unleashing her Bullet Hell ultimate skill.
- In Fallout 3, raiders and especially super mutants are often heard taunting foes and laughing maniacally in combat.
Super mutant: Hurry up and die! I'M HUNGRY! HAHAHAHAHA!
- In Sins of A Solar Empire, Ragnarov Titan's captain attack order quote is literally "I put the laughter in slaughter!"
- Flippy from Happy Tree Friends when he goes Ax-Crazy.
- Nora is a Genki Girl Blood Knight who is cheerfully enthusiastic about everything- including slaying monsters. Weirdly, she's on the side of the heroes.
- On the villains' side, Tyrian enjoys the thought of murder and violence, and engages in psychotic bursts of laughter often when cracking jokes about it. When carving up a Beowolf that tried to get the drop on him, Tyrian's anger and sadness at being referred to as a disappointment suddenly slips into bloodlust as he engages in more psychotic laughter while crying his eyes out at the same time, disturbing even Cinder.
- Insanity Wolf references this trope (three words away from word-for-word, even) during one of his verses of his Animeme Rap Battle against Courage Wolf.
- The Slaughterhouse Nine in Worm are all about this trope, especially Jack Slash, Bonesaw, and past member Chuckles.
- In his last scene, Hank Scorpio in The Simpsons grabs a flamethrower and jumps down to battle a bunch of soldiers invading his secret lair. He laughs maniacally as they all desperately run for cover, and while Homer is leaving you can hear Scorpio shouting to him that he's "missing out on some fun!"
- One episode of Drawn Together features a sickeningly-sweet Strawberry Shortcake clone who's actually committing a Holocaust. But, she reminds us, "You can't spell slaughter without laughter!"
- The 1961 Popeye cartoon "It Hurts Only When They Laughs" has Olive making Popeye and Brutus laugh while she's doing the dishes so she'll know they're not misbehaving and fighting. However, while Olive is doing the dishes, Popeye and Brutus are beating the living hell out of each other—and destroying the living room in the process—while laughing. The boys lampshaded it at the end in Popeye's ending theme tag:
Popeye: You're not a riff-raff...Brutus: If ya fights and ya laugh...Popeye: With Popeye the Sailor Man! (toot toot!)
- The slap-happy spider in the 1942 Warner Bros. cartoon Meatless Flyday sees the fly he's trying to catch hiding out as a bride on a wedding cake:
Spider: Tricky little cuss. (chuckles) He kills me! (laughs; does take) I'll kill him! (laughs harder)
- The Inspector cartoon "Plastered In Paris" has the Inspector and Sgt. Deux Deux in their squad car chasing a villain named Mister X, who sprays a cloud of laughing gas at them. Unable to see, the Inspector and Deux Deux crash head-on into a tree. Their following dialogue is delivered while they are laughing uncontrollably:
Inspector: What's so funny, Deux Deux?
Deux Deux: I think I broke my back!
Inspector: You think that's funny?? I...I fractured my leg!
Deux Deux: Does...does that hurt you?
Inspector: Of course, you idiot! The pain is unbearable!