Fanboy

fanboy, n., adj. a mildly derogatory reference to an avid fan of any particular type of science fiction or fantasy lierature, comic, movie, or game; often preceded by "drooling" as an intensifier.
Ex: /I am NOT going to a Trek convention. The thought of being surrounded by drooling fanboys scares me. See otaku. [BAL]
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Addendum: Characterized by their tendency to cluster with other fanboys, their lack of personal hygiene, and their inability to think about anything outside the context of the focus of their fannishness. [BAL]
Addendum #2: Note that the derogatory nature of this term is not from the actual hobbies or fandoms they have, but the tendency for a stereotypical fanboy to think about their fandom exclusively above all other topics and social interaction. It's not the fandom that makes one a fanboy, it's how obsessed one gets with it.