Anti-fan
Anti-fans' targets are various. The most usual target is entertainer. There are a lot of anti-fans' website for the entertainer who they dislike. E.g. Some anti-fans oppose a form of music, movie, athlete, politician, political party, TV series, idea etc. Surprisingly, the number of anti-fans tends to be proportional to the target's  popularity. Thus, the number sometimes becomes a yardstick of star's popularity.