Poserdom and the behaviour that surrounds it is an interesting phenomenon of social behaviour of modern subcultures. "Poser" is the common term for someone who regards himself or herself as part of a particular subculture (punk rockers, hackerdom, metalheads, Star Trek fandom, whatever), but for whatever reason isn't deemed worthy by his or her peers within said subculture. This usually results in a vicious circle, where the poser keeps trying harder, and the established members of the crowd will reinforce their views that he or she is a lowly maggot, not worthy of their esteem. It usually ends with the newcomer either leaving in frustration with a smashed self-esteem, or the in crowd changing their opinion for whatever reason.
While people regarded as posers are sometimes quite annoying, there's a simple behaviour pattern behind this: When you've just found yourself a brand-new identity, you need some time to adjust, to fit yourself into the new mold you've just decided you want to live in. In this adjustment period, most people overcompensate to the point of trying too hard: A newly-hatched hackerling won't open his mouths without an entry from the Jargon File coming out and the young punk-to-be will look as if she just stepped out of a time machine from 1986. They won't hold any opinion that conflicts with the paradigms of their chosen subculture's accepted groupthink. Mainly it comes down to insecurity, which is quite natural when someone is undergoing a (real or illusory) change in identity. Usually, they're just desperately trying to adapt and fit in, without seeming too alien from the subculture in question.
I propose that the collective arrogance of a subculture is directly proportional to its tendency to stick the poser label on its new members. On one end you'd have sci-fi fandom (which tends to accept pretty much anyone who's a bit freaky and reads too much / watches too much of a particular sci-fi universe), and on the other end you'd have computer geekhood (which invents words like "geekhood" to distinguish itself from the normals).