The protagonists of the Marquis de Sade's The 120 Days of Sodom, as well as many of the men in the prostitutes' stories, like to rape, torture, murder, financially ruin, and otherwise harm innocent people, for pleasure.
In Orwell's Nineteen Eighty-Four, a member of the Inner Party admits that unlike the older totalitarian movements of the early 20th century such as the Nazis and Communists, who still clothed their rhetoric as fighting for a utopian cause, the Party of Oceania is openly nihilistic and completely unapologetic that it isn't looking forward to improving the world, only seeking power for the sake of power, oppression for the sake of oppression. Ironically, this is the same reason why the nameless prole woman sings: just for the sake of singing.
In A Brother's Price, Keifer Porter is too stupid to have any long-term plan or reason for his sadistic behaviour, he just enjoys causing pain. It is later revealed that some greater mind was behind his more rational evil deeds
"I know what is right and approve, but I do what is wrong."
A Song of Ice and Fire - The series has some minor villains, who seem to be along just for their own sick pleasures. The worst ones would be the huge rapist knight Ser Gregor Clegane (among countless other atrocities sickening in nature), the inhumanly cruel outcasts in the Brave Companions, aka the Bloody Mummers, sadistic Ramsay Snow/Bolton who has torture, rape, flaying and hunting women on his resume, among other atrocities and the heartless boy-king Joffrey Baratheon, who practically revels in his power and prefers to make people fear him. This is deconstructed, as performing senselessly evil acts doesn't work in the long term, Joffrey executing Ned Stark starts a war with the North, and the evil acts of many of the worst characters come back to bite them (the Bloody Mummers are being hunted down for their atrocities).
In the Abarat series, Christopher Carrion enjoys walks on his island full of gallows, releasing unnamed horrors from the deeps of the ocean, and torturing people by allowing his own nightmares to feast on their fear.
Inverted in The Acts of Caine. The bad guys always act out of self-interest, ideology, or pure hedonistic lust. The protagonist is the one who, for shits and giggles, escalates conflicts almost compulsively. So far this includes "escalating" a verbal argument into a lethal fight, a skirmish with an ogrillo tribe into ethnic cleansing, and a minor political conflict into a civil war. (And the bad guys are still worse.)
In Alex and the Ironic Gentleman, Charles, the villain of the train, admits that their demonstrations of the life-sucking machine are mostly motivated by their desire to "scare the bejesus" out of Alex. Their other actions are also motivated by enjoyment of being evil.
Venandekatra the Vile in the Belisarius Series seems so evil that one wonders if the writer was doing a whimsical exercise in how to create the most evil villain.
Organizations with essentially the same motives as Nineteen Eighty-Four's The Party are a recurring element in the satirical horror novels of Bentley Little. e.g. The Store is about a Walmart-esque retail chain that goes far out of its way to be as oppressive and cause as much unnecessary suffering as it can; The Association is about a homeowner's association that does the same; The Policy is about an insurance company that does the same.
The protagonist in Edgar Allan Poe's The Black Cat starts hurting people and animals around him For The Evulz or, as he himself puts it: in the "spirit of PERVERSENESS". Poe's perverseness is an odd supposed psychological motive (but perhaps related to negative suggestion) that goes a step further than For The Evulz, inspiring not just morally wrong acts harmful to others, but any kind of irrational and wrong acts even just harmful to oneself; inspires one to do anything they shouldn't just because they know they shouldn't. The protagonist hangs his pet cat, because he knows that it's just about the worst thing he could possibly do.
One morning, in cool blood, I slipped a noose about its neck and hung it to the limb of a tree; hung it with the tears streaming from my eyes, and with the bitterest remorse at my heart; hung it because I knew that it had loved me, and because I felt it had given me no reason of offense; hung it because I knew that in so doing I was committing a sin — a deadly sin that would so jeopardize my immortal soul as to place it, if such a thing were possible, even beyond the reach of the infinite mercy of the Most Merciful and Most Terrible God.
In James Beauseigneur's Christ Clone Trilogy when Decker, the viewpoint character, asks The Antichrist ( Christopher Goodman) why he does what he does when he knows he's going to lose, the reply is "Because it feels so good to twist the nose of God!" The same Antichrist later muses how an eternity in Hell will be tolerable in the knowledge that he tricked millions of people to join him there so he can listen to their screams forever, including his own parents.
In Perelandra, Satan himself is this. While he has real (and deeply malicious) ambitions, when he can't move directly toward them he's just as happy torturing small animals or tearing up the turf, so long as he can hurt something. When Venus!Eve is around he's eloquent, logical, and persuasive, but when she's not one of his favorite pastimes can be summed up by this exchange: "Ransom. Ransom. Ransom. Ransom." "What?" "Nothing. ... Ransom."
Averted in The Screwtape Letters. The preface to later editions notes avoidance of "the absurd fancy that devils are engaged in the disinterested pursuit of something called Evil (the capital is essential). Mine have no use for any such turnip ghost. Bad angels, like bad men, are entirely practical. They have two motives. The first is fear of punishment.... Their second motive is a kind of hunger."
Averted again inside the letters themselves, which deal with the attempts by a devil to tempt a man to damnation from within C.S. Lewis' own eschatology. Screwtape, a senior devil, advises his junior Wormwood that big, bad, horrible evil is not the best option. He wants the petty, small, low-grade denial of Grace and Salvation - just enough to damn a man, but not enough to make him willful and defiant enough to repent.
"It does not matter how small the sins are provided that their cumulative effect is to edge the man away from the Light and out into the Nothing. Murder is no better than cards if cards can do the trick. Indeed the safest road to Hell is the gradual one—the gentle slope, soft underfoot, without sudden turnings, without milestones, without signposts."
In Mere Christianity, Lewis offers a theological deconstruction of the trope: It is possible to do good simply for the sake of doing what is right, but nobody does evil simply for the sake of doing what is wrong; evil deeds are merely the pursuit of some good in the wrong way.
While Nyarlathotep from H.P. Lovecraft's Cthulhu Mythos often works to fulfill the wishes of the Outer Gods or release the Great Old Ones, a lot of the times he seems to be messing with mankind for no other reason than his own amusement. In "Nyarlathotep", he seems to be destroying the world without any actual motive. In The Dream-Quest of Unknown Kadath, his goal is apparently to snatch off the earthly gods from their scented revels in the glorious sunset city purely to screw with them. Also, in spite of apparently sending Carter off to achieve this goal, he betrays Carter for no apparent reason other than, again, to be a real dick. The ways of the Outer Gods are essentially beyond human comprehension. In "The Dreams in the Witch House", he appears as a black-skinned expy of Satan. He's even worse in other authors' appropriations of the character.
While Nyarlathotep may have had a reason to return the Gods of Earth to Kadath (that's where they're supposed to live), him sending Carter to accomplish the task for him and subsequently betraying him serves no point other than being a dick. Especially since in the end it's revealed he's powerful enough to return the Gods to Kadath with no effort at all.
Carcer from the Discworld novel Night Watch. "The sort that joins up for the looting, and that you end up hanging as an example to the men". Possessed of a pair of shoulder demons, in competition with each other.
Edgler Vess from Dean Koontz' Intensity is a self-proclaimed homicidal adventurer, who loves to kill just for the sheer intensity of it. Vassago from another Koontz novel Hideaway kills people so he could be reincarnated as one of the demon princes in Hell (it's not clarified what he would gain from it). As a matter of fact, simply every villain in every Dean Koontz book ever written.
In Borges's Deutsches Requiem, the Nazi murderer zur Linde tortures a Jewish poet until he kills himself purely For the Evulz; indeed, it seems that zur Linde thinks that by destroying David Jerusalem, he can destroy whatever goodness remains within himself, and that's what he deliberately sets out to do. At the end, zur Linde is actually happy that Germany is being defeated and destroyed, because he believes it will lead to a world of pure violence, warfare, and cycles of domination, and that's worth the death of both himself and his nation.
The various Great Enchanters in the Diogenes Club series can be like this.
At first sight the most prominent example, Derek Leech, is an exception; he is a yuppie (albeit a demonic one) who does evil in pursuit of profit. On closer inspection, however, he pursues profit because this maximises how much unpleasantness and misery he can spread.
Dr. Mabuse, who was inspired by Fantômas (see below). In addition to spreading fear, however, Mabuse wants to destroy the world... and laugh maniacally over the rubble.
In Dragon Bones, the villain has a slave who is magically compelled to obey him. One would assume that poor slave wants to break free and do a Heel–Face Turn, but no, apparently it is the other way round and the villain keeps the sadistic urges of the slave in check, who would torture random people for the evulz, while the villain has a more thought-out plan.
The Order of the Blackened Denarius from The Dresden Files are explicitly stated as being out to inflict as much chaos, death, and destruction as possible, and are responsible for inciting numerous plagues, wars, and other disasters. Shagnasty, if anything, was even worse than the Denarians, deliberately striking out at hapless bystanders and opponents far too weak to hurt it, simply to show off how much pain it could inflict.
Both of these examples, however, might have ulterior motives beyond the Evulz. It's noted that the Denarians gain power through the pain and suffering of others, and Skinwalkers like Shagnasty draw strength from the fear others feel for them - doing horrible, nasty things increases this fear, and thus the Skinwalker's power.
Fantômas: the valuables he steals is just an added bonus, what he really enjoys is to spread fear.
Fate/Zero has a cast full of characters that fight for various ideals but the Evil Duo of Ryunosuke Uryu and the Gilles des Rais do what they do for the sake of their Mad Artist streaks and for the sake of evil. Gilles des Rais manages to humanize this trope somewhat in that the death of his beloved Joan of Arc broke him so much that he snapped and became a serial killer to cope with the pain, but eventually and slowly began to love killing by the time he's summoned into the nineties when the story takes place, though in death, he realizes he never should have become a serial killer and lived For the Evulz. Ryunosuke on the other hand just loves killing and always has, and worse than that, loves killing children and turning peoples' bodies into art. Ryunosuke technically has an ideal in that he loves death, even being happy at his own death but he fully admits that he knows what he is doing is considered evil and loves it. Worse than that, he thinks God should like him for it since God must be amused by both the "heroes and villains" in the world.
Bellatrix Lestrange always seems to have way too much fun killing people, breaking their stuff and torturing innocent people into insanity. Much more obvious in her movie portrayal, where she spends quite a bit of her screen time laughing maniacally. Even more obvious near the end of Half Blood Prince, where while all the other Death Eaters are just calmly leaving the castle after Dumbledore's been killed, she decides to cause as much destruction as possible, clearly enjoying herself.
The werewolf Greyback. He takes to infecting small children because he thinks they will be more likely to join his cause if they are infected young. He claims motives such as overthrowing the wizards, but most of his actions are purely for the fun of destroying people. According to the Harry Potter Lexicon, all Dark creatures (including werewolves) harm people for the sake of harming people, not for survival like normal animals. Greyback is unique because he hurts people in his human form.
In The Hitchhiker's Guide to the Galaxy, Vogon poetry is considered the third-worst in the galaxy. The Vogons' first attempts at composition were a blundgeoning attempt to prove themselves as a properly evolved and cultured race, but now they do it out of sheer bloody-mindedness. One Vogon explicitly states he writes poetry simply because hearing it hurts people and bring his cold, heartless exterior into sharp relief.
Jonathan Teatime in the novel Hogfather: "People say I'm the kind of person who would just as soon kill you as look at you, but that's not true. I'd much rather kill you."
In Death: A number of times in the series, the murderer or criminal says that s/he is doing what s/he is doing because s/he can. If that's not another way of expressing this trope, then what is?
Melisande Shahrizai, of the Kushiel's Legacy series. When asked why she started a civil war and tried to conquer her own country she responds with, "Because I could."
The vampire Lestat from the novel by the same name and others by Anne Rice. When asked why he is so cruel, Lestat simply states that he likes it and enjoys it.
In The Millennium Trilogy, "Zala's" real (though unstated) motive for running a ring of sex-traders seems to be that he's simply a misogynistic sadist who enjoys dominating and hurting women. Even The Dragon thinks that the sex-trade is too high-risk for its mediocre profits and that they ought to do something else. This also seems to be his main reason for horrifically abusing Lizbeth's mother (playing cruel mind games and beating her into permanent brain damage), and it's clear from the manner he draws on Screw the Rules, I Have Connections! that he relishes making life difficult for the people who have to bail him out.
Croup and Vandemar from Neverwhere appear to have this motivation. They kill people horribly on a professional basis, and are quite proud of this. For recreation, they kill people even more horribly. Croup also eats works of art.
In The Night Angel Trilogy, one of the most dangerous Wetboys out there is Hu Gibbet. While he can be considered a Psycho for Hire, the main reason he does his work is because he enjoys it: working for the criminal organization that basically runs the city from the shadows lets him kill often, without having to worry about getting pursued by law enforcement. The thing is, he really, really, REALLY enjoys killing people. Especially when it comes to large groups of people. Shortly before he is killed, he is genuinely concerned that he has been given a contract larger than any he has ever been given before. He's worried that he might enjoy himself so much that he might get sloppy and miss a few of the targets, which is the ultimate no-no for a wetboy.
There needs to be a special place here for Quinn Dexter, the central villain of Peter F. Hamilton's The Night's Dawn Trilogy. A cunning, vengeful Satanist that was cast out of his coven and exiled on a fresh colony many light-years from Earth for being too devout. He gets possessed by a soul returning from the dead, only for him to eventually scare the possessing soul sh*tless and re-assert control of his body while maintaining the Reality Warper abilities that possession brings. From there, it's a jolly journey back to Earth to exact terrible vengeance on his former boss, gathering up followers and bringing slow, agonizing destruction to entire planets as preparation for ending the Universe. Because, hey... that's what Satan would want.
An awful lot of misbehavior in the Nightside series, from heinous torture of innocents to the merely rude, is attributed to the "just because he/she/it/they could" motive.
Cal, the dominant who abused submissive Jay in M.Q. Barber's Playing The Game series, is a pure sadist, who enjoys causing pain simply because he can, regardless of whether or not the recipient is also enjoying the experience. When called out on it, he gets vindictive.
BKR of Rod Albright Alien Adventures certainly counts. His plan to create a Merged Reality between our world and Dimension X, and then his plan to disrupt space-time so time itself will stop, would have effected him just as it did everyone else. His Arch-Enemy Grakker explicitly says that he knows' that he would also be affected, but as long as he can hurt other people, he just doesn't care.
At the end of the The Saga of Darren Shan, it is revealed that Desmond Tiny's plan - fortunately foiled by Darren - involved magically fathering both Darren and Steve and giving the Vampaneze the fire coffin (so that they could find the Vampeneze Lord) and the Vampires a special stone that would help them in their hour of need (made from the brain of a dragon). He then manipulated events to ensure that Steve and Darren both went to see the Cirque du Freak, paving the way for Darren to eventually become a Vampire Prince and Steve to become the Vampaneze Lord. He then pits the two against one another, insisting that the vampires only have three chances to kill Steve before he overthrows the Vampires and later tells them that whichever boy won - Darren or Steve - would become the Lord of Shadows and kill all of their friends. When the vampires used the stone gift to create more vampires, it would create a new breed of violent ones. The reason he did all of this? He looked into the future and saw that things were going to be too peaceful for his liking, so he set the stage for a lot of chaos to amuse him.
Those responsible for the Dome in Under the Dome. They're compared to children torturing ants.
Randall Flagg in The Stand and his other roles in the Stephen King universe. He's not really seeking out anything concrete with his actions: he just likes spreading chaos and misery. He'll enjoy some of the fruits of being an all-powerful sorcerer, but he mainly just likes mucking things up.
The title character of Mr. Mercedes enjoys causing death and destruction on a large scale for his own personal amusement.
In Carrie, Sue Snell speculates about Chris Hargensen's motivations, and comes to the conclusion that she just wanted to destroy Carrie White for its own sake.
In The Stoneheart Trilogy, the Walker hunts down glints and steals their heart stones (which slowly sends them insane), not out of any duty to the London Stone, but because he finds it entertaining. And to make it worse, the Walker displays the stolen heart stones on the walls of his lair.
The guiding philosophy of Acheron Hades from the Thursday Next series, and probably the rest of his family as well. He even says as much in one of the quotes from his book "Degeneracy for Pleasure and Profit"; despite the title he feels that crime-for-money is rather crass and much prefers evil for evils sake.
The sadistic serial killer in Spider Robinson's novel Very Bad Deaths exemplifies this: He inflicts horrible cruelties upon his victims because he enjoys it. He derives the same sense of satisfaction from cruelty than most people get from kind ones.
Warrior Cats: Okay, so we know that Sol wants to use the Three's powers to gain control over all cats living around the lake and eliminate belief in StarClan, but his manipulation of the Twolegplace cats doesn't have anything to with his plans, and was seemingly done for the hell of it. Plus, he doesn't seem that committed to his goal, doesn't approach it with much urgency, and seems to get way too much enjoyment from messing with the main characters' minds.
In Wildwitch: Lifestealer by Lene Kaaberbol, it is revealed that the father of one antagonist kickstarted her Start of Darkness by killing her beloved pet bird, and having it stuffed and mounted on a branch. Because she complained that the boarding school wouldn't let her take her pet bird with her. One wonders how the hell he thought that would make the child more compliant. The fact that it did sort of work and she just went very quiet indicates severe psychological damage, which one would hope the father did not intend to cause.