The collective outlook and behavior of a group of people concerning a subject (movies, games, hardware, comic book characters, etc.) which when challenged results in an antagonistic, passionate, and unreasoned response.
Rampant Fanboyism can be found on most internet message boards when such hot button subjects are discussed. You know a fanboy when you see one.
Fanboy 1: "Stupid people didn't get this movie"
Fanboy 2: "If you didn't like the movie, you should'nt come here and trash it."
Fanboy 3: It's unrealistic because.....___(fill in the blank about how this movie about flying superheroes is unrealistic.___"