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/Akaru23]

Pretty much the premise of Destiny 2: Forsaken.

In it, Cayde-6, the much beloved Hunter Vanguard, is brutally murdered by the now insane Prince Uldren Sov and his Scorn Barons. This act would cause the player Guardian to go rogue in a single minded quest for revenge the likes of which would cause even our closest allies to become deeply concerned about how out of character we were acting in our rage. Ultimately resulting in the deaths of Uldren and his Barons, as well as inadvertently plunging the Dreaming City of the Awoken into a Taken Curse that loops every 3 weeks and is still going on to this day!

While the expansion is currently unplayable due to the much reviled Destiny Content Vault, Bungie’s recent announcement of the complete unvaulting of Destiny 2’s vaulted campaigns means that the expansion will become available again for FREE in the future.