HP fandom is pretty wierd cultish, especially around ROWLINGS terf-iness.

another genre is supernatural fandom , pretty cultish, mostly around how the fans think the actors were in a gay relationship, when they are not. to the point it creeped out the actors(jensen and jared, and misha) and one point i heard some of the guess actors were met with death threats from said fans, who also developed parasocial relationship with the actors.