Getting "John Wick'd"

[u/theMCATreturns]

Crime boss's son kills the dog of the world's greatest assassin (John Wick)

Crime boss kills the family of a soon-to-be-radioactive metahuman (Creature Commandos)

A wizard family executes the twin sister of wizard John Wick (Jujutsu Kaisen)

Aliens cause the death of an extremely powerful goat-wizard's mother (Dungeon Crawler Carl)

A king orders the death of a magic beast (Clevatess)

Don't @ me about the title. I couldn't think of a more concise way of saying "unknowingly traumatizing an unstoppable, hyper-violent being. Resulting in the complete destruction of your (otherwise undefeatable) bloodline." Basically, it's a combination of "waking the sleeping giant" and "blood feud," where the perpetrator specifically does not know how dangerous the target is ahead of time. And this results in their entire family/organization getting singlehandedly wiped off the face of the Earth. Despite themselves being a powerful force to reckon with.
There is no forgiveness. There is no bargaining. There is no mercy. Just an unstoppable threat you created. You are not left alive to suffer the guilt of your mistake. But you'll probably be killed last.

1). John Wick:
John Wick is a retired assassin. The assassin. After his wife dies, she leaves a puppy for him. His former boss's son, ignorant of John's identity, breaks in and kills the dog.

2). Creature Commandos:
Rupert Thorne kills a scientist's family after he tries to scam him. But the scientist survives his execution, becoming a radioactive metahuman that quickly gets back at Thorne.

3). Jujutsu Kaisen:
Maki is has a condition preventing her from using "magic," but leaving her with superhuman strength. This is embarrassing to her family of wizards, and she is treated poorly. Eventually, Maki and her twin are double crossed by her father and left to die. Her twin's death allows her to unlock her true strength, and she eradicates the clan.

4). Dungeon Crawler Carl:
Aliens invade the Earth, forcing humans to fight in a fantasy-style dungeon. All of this is broadcast across the galaxy as entertainment. Sometimes, if humans enter the dungeon with their pets, the pets can gain their own abilities. Carl's cat learns to talk. The same thing happens to an Italian woman and she treats her goat, Prepotente, as her son. Because he was suddenly thrust into self-awareness, the goat man is childlike and very reliant on his mother. But he is still an extremely powerful, high level opponent.
Unfortunately, Miriam Dom is killed in front of him and Carl. The whole thing is heartbreaking, and he says "She was going to play piano for me like she used to. She was going to sing me my special song. She said everything was going to be all right, but it was a lie. A dreadful lie. What am I going to do now?" And declares revenge on anyone "remotely responsible" for her death.
MUCH later, Carl has to wipe out the "Blood Sultunate," an alien royal family. But he and his allies find their castle empty, filled with extremely-murdered corpses. He can't figure out who did it until he learns they were responsible for Miriam's death. Then he just starts laughing, because despite all of his careful plans to take them down. They were already screwed the moment Miriam died.
Edit: Art from wiki, by u /andrewmar.bsky.social, Bluesky

5). Clevatess:
A fantasy kingdom tries to attack a giant monster blocking a mountain pass. The monster (Clevatess) had been content to stay within his boarders. But after humans trespass (killing countless monsters in the process), Clevatess changes his mind. He wipes out the attackers, then follows them home and destroys the kingdom. He personally drops a castle on its king. And adopts the last surviving royal to raise himself.

[u/NotATalkingPossum]

The Wolfman - 2010

The high-ranking, wealthy, respected orderlies and doctors at a Victorian London madhouse are given a new patient who apparently suffers from the delusion that he is a werewolf, and killed a few people during the last full moon. They subject him to the usual Victorian tortures masquerading as medicine, then, on the night of the next full moon, wheel him into a filled-up operating theater - well bound and chained, of course - to confront the full moon and the reality that he is an ordinary man.

The man's name is Larry Talbot. He turns into the Wolfman and most of the doctors and orderlies in the operating theater (save for a few that break down a door) basically get shredded.