Unfannish

(adj.) Not fan-like or not fannish.

Unfannish is most often used in a tongue-in-cheek manner. ("You're skipping the con for a baseball game? How unfannish!" "There are no books in this room. It's unfannish!")

The term is sometimes used in a condemnatory fashion, meaning not befitting of a fan. ("Bigotry is unfannish.")