The Harry Potter fandom, at its height, was a positive treasure trove of cows, most of whom seem to have largely vanished off the face of the Earth. There were conspiracy theorists, pedoforks, spoiler-giving weens, literally homicidal shippers, appearances by Andrew Blake and similarly loathsome people, and even the head of one of the two largest fan sites had a memorable shit-flip when he tried to publish a reference book for the series without J.K. Rowling's permission and they predictably wouldn't let him. In my mind, though, nobody could out-cow "The Grangerverse," a pseudo-cultish outfit led by a person who called himself "Pstibbons."
Pstibbons was completely in love with Hermione Granger (and from what I remember he turned out to be a middle-aged man for maximum creep factor, though I may have gotten him confused with someone else) and he and his followers had a... rather offbeat theory about the books: Hermione, not Harry, is the actual protagonist, with Harry himself being a sort of decoy, or as they termed it "frontkick." They had a special loathing for more conventional fans who believed that, y'know, the guy whose name is in the title is the main character, and undertook a sort of guerrilla campaign to write "subversive" fanfics about Hermione taking what was rightfully hers.
Naturally, they were all atrocious. The Grangerverse believed that Ron was nowhere near good enough for Hermione, and most of the Grangerverse stories feature him meeting a grisly end, often involving rape. Harry and Ginny came in for bashing aplenty as well, but their fates were usually less visceral. A number of the stories also contained gratuitous gay sex, and there were at least two that featured Hermione giving up magic entirely to become a katana-toting, tracksuit-sporting mercenary, totally original you guys. Truly,. the Grangerverse are the counterculture icons society needs.