A person who is not a fan of something, but can't help but be drawn to the subject. One who hates a band, form of music, movie, or movie series, politician, political party, car, TV series etc. so much that he/she likes to hate it. An anti-fan is very knowledgeable about the subject they love to diss.
Dude, Jeramy is such an anti-fan of saw, he owns all the DVDs and can't wait for Saw IV.
Mandy is such a Green Day anti-fan so much that she goes to their shows just to boo them.