One who manifests much affection for the genre of shooting games; first person shooting games, to be fastidious.
Guy 1: "Dude, where that dweeb, Mark, at?"
Guy 2: "Probably in his basement, he got that new game, Modern Warfare 2."
Guy 3: "Wow... The dudes a complete FPSF."
Someone absurdly obsessed with first person shooters.
Guy 1: Man...all billy does is play Shooting games.
Guy 2: Yea hes a fpsf.