Someone whom does one or more of the following:
1) Has an obsession of a certain object, thing, or fad. (Dragonball Z, Baseball, Video game consoles, Yo-yos.
2) One that does not think that his obsession or hobby (if they didn't fit the first one) will make him any real friends or perhaps get him laid
3) One that defends that obsession beyond all hope and logic. Also, one that cannot back up their statement with anything but flame bait
4) One that takes his obsession beyond comprehensible levels of sanity.
Lets use all four in context: (Note: I am not a nintendo fanboy or a bush hater. These are hypothetical situations one might observe these things happening)
1)Fanboy: So, did you see the episode of Xena:Warrior Princess last night? OMG, Lucy's using the Hermina Blade! I've only read that in the novels!
2)Fanboy:Dude, Sailor Uranus is so freaking hot!
Other guy: Dude, get the hell away from me.
3) (Two examples)
Guy 1: Well, the gamecube hasn't been doing so well this year....
! DID YOU JUST SAY THAT THE GAMECUBE SUCKS?!?!?! YOU SUCK! YOU AND YOUR SONY FANBOYS CAN ALL BURN IN EVERLASTING HELL ALONG WITH GATE'S X-BOX!!!!!
Guy1: Hmm....the president has been doing a lot towards the economic situation....
Guy2: Yeah! Bush sucks balls!
Guy1: I didn't say that...
Guy2: Bush is a stupid idiot.
Guy1: You fanboys should be shot.
4)Fanboy: And you can obviously see that Rikku
in FFX-2 is obviously not wearing much in this scene. The humidity from the sun and the build up in the room must be from that. Yeah....also.... (goes on for half a year...)