A Fandom that is dedicated to hating a work or author, instead of celebrating it. Sometimes they view the work as So Bad It's Good (to the ire of more traditional fans); at other times, they just loathe it outright, but enjoy making fun of it. Some works have the dubious honor of producing hatedoms larger than their traditional fanbase.
Of course, for optimal snark it's best to have actually read/watched/played/listened to some of the hated work, but some people have gone so far as to produce derivative works capable of standing on their own with only a general knowledge of the original. On the other side of the equation are people that view the work several times over, memorize all the supplemental minutae, and write senior thesis level dissertations over the underlying themes and structure because they hate it so much.
In cases where members of a Hatedom also hate the fans of said work, they would be Fan Haters. It should also be noted that a Fan Hater isn't necessarily a member of a Hatedom; it is quite possible to be a fan and hate other fans of said work, a phenomenon that can also be blamed on the Fan Dumb (i.e. being exposed to too much of it). Fans of a work are likely to view its Hatedom as a Hate Dumb.
When you have a hatedom within a fanbase, it's called Broken Base. When you hate something that wasn't aimed at you in the first place it's a Periphery Hatedom. Typically, works that are more well-known are more likely to produce a Hatedom. After all, it's much easier to ignore more obscure works that you happen to dislike—and, if not many people have not even heard of the work, then finding a fellow hater to commiserate with would be next to impossible. Thus, this trope is closely related to Hype Backlash.