Canonically happens quite a bit in the BattleTech universe. The Kentares Massacre and the Word of Blake's Jihad are just two major infamous examples (the former historical, the latter rather more recent) that virtually anyone in the setting could immediately name.
In Dungeons & Dragons, the Draconomicon states that even good dragons are prone to this. Any disrespect, even if it appears minor or an individual case, is magnified when made towards a dragon due to lesser mortals not knowing their place and their long life where they associate it with a long series of insults.
There are also marids, genies of elemental water. Apparently, offending one in any way is a crime in their society if you aren't a marid. (And they barely tolerate being offended by other marids.) Of course, they're such incredible egotists that every one of them (that is not an exaggeration) has at least some title of nobility, if not royalty.
In the Dungeons & DragonsRavenloft setting, the gothic Powers That Be in control of the place love answering pleas for vengeance - but freely disregard the scale of the supposed wrong. A lot of the campaigns revolve around some greedy or prideful person successfully calling down a curse of undeath or torment on someone for an imagined slight or trivial grievance.
Plenty of darklords are heavily into this trope as well, such as Hazlik, who's plotting cross-planar genocide against his own ethnic group because a few of them once forcibly tattooed his head and called him nasty names.
Err, Hazlik's grudge is on deeper grounds then that. His colleagues forcibly tattooed his head with feminine gender-slurs, stripped him of his rank and possessions, and declared his society had not only free reign, but the legal obligation, to kill him on sight. This was punishment for a rival of his successfully claiming he had raped her boyfriend — except she and he had trapped Hazlik to get him accused of this, taking advantage of his crush on him. He ended up in Ravenloft because he promptly ambushed them, cut the man's heart out, fed it to the woman, and then killed her too.
The Forgotten Realms campaign setting has that, combined with a Self-Inflicted Hell. Did you worship an evil god because it was the culturally accepted thing to do where you came from? Then you're going to that God's hell, even if you never really did anything evil or you never even knew of a good god you could worship. And it won't be pleasant ('cause none of the evil god have pleasant afterlives for their followers, making one wonder how they get followers at all. Worship me! And win eternal torment). Were you an atheist? Then once you die you get to spend a LONG time having your soul slowly destroyed, becoming part of a wall, gradually losing your memories and personality till there's nothing left.
This is actually explained in most settings: The denizens of the evil planes really don't mind being turned into demons. They get to torture and kill people for fun and have the chance for advancement. Sure, being larvae or dretch or mane or lemure isn't much fun, but on the other hand you get to be immortal and (eventually) quite powerful. "Here's the chant: Tanar'ri like bein' tanar'ri: Raw indomitable power's what's bein' a tanar'ri's really about."
The more reasonable way to put it is that they may think they want it. It's hard to imagine it would be a truly enjoyable existence. A section on "roleplaying a demon" in one sourcebook has this to say:
Have you ever been really angry? So angry you just wanted to destroy every stick of furniture in the house? Imagine having felt that way for many, many centuries, and that you have spent those centuries surrounded by creatures who not only feel the same way and glorify feeling that way, but who are sufficiently powerful enough to inflict their rage on you. Daily. In the most excruciating ways possible.
Any soul heading to its deity's plane ends up losing its memories and personalities, eventually becoming part of that plane. The wall is just absolutely bland: no reward, no torment, no one to talk to, just absolute boredom.
Well... the novel Prince of Lies, a significant portion of which took place in Cyric's (God of murder, madness, etc.) afterlife, indicated that while the hell still isn't 'pleasant', it's at least not 'eternal torment' bad. For example; Cyric's loyal worshippers in life got to be monstrous demons who tortured other souls in death! That's... that's good?
As 8-Bit Theater puts it, "This is hell. We're big on irony here."
The Drow goddess, Kiaransalee, is the Goddess of Disproportionate Vengeance
The Demon prince Graz'zt is probably the least likely demon lord to rip you apart just for existing, even opening his layers of the abyss for trade. Mention that he actually fell in love with Iggwilv, that Malcanthet turned him down, or call his domain "The Little Hells", and he will feed you to the predatory plants in his gardens.
The thing with Iggwilv is not Disproportionate Retribution from a fiend's point of view. Quite simply, one of the worst humiliations a fiend could suffer is a mortal getting the better of him. And Graz'zt is one of the three most powerful rulers in the Abyss. Basically, demons would see this as someone Bullying a Dragon and actually winning, so it was a serious blow to his pride.
One sample adventure "For Hate's sake" in the Heroes of Horror sourcebook is made of this trope. Growing up, Samuel (one of the primary villains of the adventure) was that guy who always held a grudge. Eventually he became a priest of the god of this trope himself. He then began taking revenge on all his childhood grudges (granted it's implied that MOST of these didn't involve murder). He eventually becomes complacent...so his god pulls a Poisonous Friend and summons a ghost to take revenge for him, and this time it ALWAYS involves murder. Samuel goes mad with guilt and ends up pleading with the ghost to stop, only to be (depending on their actions) killed by the PCs, who the game master leads to believe is responsible (which given that his god is also playing this trope for Samuel becoming complacent, he is, in a way).
This is why you do not steal the Relics of the Arisen-neither they nor their gods take kindly to tomb robbers, so a dormant one will likely be brought out of stasis, and he will find you. Fun Fact: The Empire of Irem didn't really have a concept of forgiveness, only revenge.
Player Characters in Nobilis are bound by the Sevenfold Precept. Harming innocents is against the law, but if anyone harms you, you are allowed to repay it sevenfold. And (at least in Second Edition), Lord Entropy includes under the definition of "harm" accepting insults from a mortal, or simply accepting an order from one. Because it diminishes a Noble's miraculous nature.
In Chuubo's Marvelous Wish-Granting Engine, Entropy's son, Entropy II, has set as one of the laws of his Evil World that none can be harmed more than three times as much as they deserve. (Why not "exactly as they deserve"? Because to Entropy II's mind, that can result in a rather nasty form of "you deserved that". Better to have a situation that evokes some sympathy.)
This is part of the reason why the Dwarves in Warhammer Fantasy are A: part of the "Gray" side of its Black and Gray Morality, and B: a dying race. They honor Revenge Before Reason to the point they are Too Dumb to Live, being willing to do things like get into a war that sees dozens of their own people dead and raze a castle that they spent years building to the ground because the guy who paid them was two and a half pennies short in his dozen wagonloads of gold payment.
The best example for the Dwarves, is the War of Vengance Or the War of the Beard by the Elves. It all started when the Dark Elf raiders disguised as High Elves attacked some Dwarf traders. The High King demanded compensation from the High Elves, but arrogant Elf king Caledor II refused and had the dwarf ambassadors beard shaved. This was a considered the greatest insult to the Dwarves, who declare and all out war on the High Elves. The resulting war shattered the two Empires, and it ended with the Caledors death by High King Gotrek who took the Phoenix crown as compensation, and the High Elves were forced to withdraw from their colonies in the Old World to defend Ulthuan from the Dark Elves.
Prince Sigvald once burned down an Imperial City. The reason? He didn't like the taste of their wine.
The Steel Cobras Space Marine chapter worshipped the Emperor as an animal totem. The penalty for following the Imperial state religion in the wrong way? They were duly excommunicated, and any Imperial force to see a Steel Cobra is permitted, nay required, to shoot on sight and leave asking questions to the Inquisition.
All this while every single Marine chapter worships the Emperor in a way not sanctioned by the Ecclesiarchy, and some are much weirder than the Steel Cobras without being censured. Even worse, Space Marines don't have to worship the Emperor (as the geneseed comes from the Emperor), they just have to be loyal to him, and some Chapters are rather open about it.
All this just shows that all it takes to accuse a Space Marine chapter of heresy is one dumb Inqusitor and some bad luck. Even First Founding chapters are not immune to this as Months of Shame show.
The Carcharodonschapter of Space Marines◊ are in love with this. After gaining control of the enemy's holdings (the Tranquility system) at the end of the Badab War, they exterminated every single person who was not of recruitable age, and forced the rest to fight to the death to determine which of the tiny percentage of survivors would get to join their chapter. After that, they stripped the system of all useful resources and vanished.
The Black Templars Space Marines, upon learning that a few people on a planet had purchased alien equipment from traders, proceeded to massacre a significant chunk of the population. Even the Imperium usually limits the punishment for this to jail time.
Subverted with Exterminatus. You'd think blasting the planet into an unusable wasteland is a bit much, but it's only supposed to be used if Chaos or Tyranid forces have overwhelmed a planet to a point where it isn't worth taking it back (Chaos corrupts everything and the 'nids eat everything and thus can lose billions and still have a net gain, so blowing up the surface of the planet will keep them from consuming anything usable) and yes, even the Imperium has its limits for throwing men into the meat grinder. Though given how utterly dystopian the setting is, someone, somewhere no doubt has used it for less than proper or sane reasons.
There is, in that a planet got exterminated because the taxes paid didn't round up and thus the Inquisition assumed they had started worshipping Chaos. Oooops...
There is an Inquisitorial Ordo whose job is to pass judgment on whether or not the Exterminatus committed was justified. Their approval rating is less than 10%. In more than 90% occasions the Exterminatus is declared a mistake and an Inquisitor who ordered it is stripped of his rank and executed.
Imperial Guard Commissars are known particularly for their application of BLAM (fatal gunshot) in dealing with insubordination, heresy or uniform violation among hapless troops.
The Imperium has also been known to send entire regiments with a mandate to burn the planet if strictly necessary, because someone bought a Tau-made crop harvester.
Of course that's partially justified since if that crop harvester had been bought from certain other illegal sources it would cause anyone who took a bite of the crops to turn to Chaos, mutate, or get stricken with a particularly virulent Nurgle disease. If someone gets away with purchasing from the Tau they'll keep buying from other xenos until they get a Chaos artifact in a shipment.
See the above about flip-flopping. The Imperium has also been known to tolerate - or at least turn a blind eye to - limited trading with the Tau Empire provided it's kept low-key. So...Depending on the Writer.
Less Depending on the Writer and more Depending on the Inquisitor. The Inquisition is a vast organization, and they vary pretty wildly in what they'll tolerate. Some, such as Gideon Ravenor of Dan Abnett's Ravenor Trilogy, will flat out ignore some xenos if they have better things to do; others will torture you on vague suspicions (most of them are in the fluff, as they don't tend to make relatable protagonists).
Any member of the Inquisition can and will dispense these at a moment's notice depending on their mood, temperment, boredom, paranoia, or a combination of both. Inquisitor Lord Karamazov famously roasted a young preacher. His crime? Thorian inquisitors, Karamazov's peers, thought the preacher might have been the Emperor reincarnated. The boy had otherwise done nothing wrong.
Karamazov usually roasts people for far less. In his court, everyone found guilty is sentenced to death. Everyone found innocent is sentenced to death too because they wasted his time by appearing guilty while having done nothing wrong.
Woe befall anyone who crosses the Dark Angel's path. Their Interrogator-Chaplains extract confessions from suspected Fallen Angels with brutal torture. If you deny you are one, they will call you a liar then continue to torture you until you do confess, or kill you if they think it's pointless. If you confess you are one (even falsely) they will accept the apology, then kill you.
/tg/ created the Necron Lord Assholetep, "An aeons old automaton king... with the petulant impatience and obnoxious tantrums of a 7 year old child." Anecdotes regarding Assholetep state that he will obliterate entire sectors over comically trivial slights.
The Europans' general schtick in Rocket Age. They bombed Io back into the stone age (they consider this merciful), engaged in a genocidal war with the Jovians when they began using space flight, driving them into hiding, as well as constantly threatening Earth with disintegration.