I'm God fanfiction
It's when the writer takes a story and completely rewrites it with their own dumb ideas, making the characters into total messes just to show off how cool they are.
A Naruto fanfic where Orochimaru is a shy, soft-spoken boy who cries when he's sad.
A SoulEater fanfic where Maka is a prissy, overly dramatic girl who yells at everyone.
A Sonic fanfic where Sonic is a loud, obnoxious, and completely useless jerk.