Refers to two types of individuals:
1) Someone who lacks knowledge, but who tries to compensate by pretending to be very smart, by carrying around impressive looking books on science, math, literature, and related subjects. May also wear a trendy, sophisticated pair of eyeglasses.
For the most part, this type is harmless.
2) Someone who has a serious personality disorder. These types derive a great deal of pleasure by "enlightening" others with their "brilliance" and "wit".
Their primary method of operation is to use irony and sarcasm to taunt those who they believe do not live up to their standards. Virtually every word out of their mouth is some unnecessary, smartass remark.
They lack the ability to have a genuine, sincere conversation with anyone. Instead of having a healthy, balanced, back-and-forth exchange, they pontificate and talk down to those who have the misfortune of not escaping the room before they walk in.
It is a waste of time to point out to these disturbed individuals that their behavior is obnoxious, as they will inform you that you simply lack the ability to understand their "superior" view of the world.
Basically, it's someone who thinks that being an argumentative wiseass somehow makes them cultured and fun to be around, and that shouting at the rain and being disagreeable for the sake of being disagreeable somehow makes them substantive.
Me: "I think I'd like some barbecue sauce with my chicken nuggets."
Pseudo-intellectual: "What part of the chicken does the nugget come from, and are the chickens free range, and is the barbecue sauce the same red color as the blood that runs through the streets of Baghdad because of the evil American capitalism and imperialism that empowers greedy coporations such as McDonald's to exist?!"
Me: "Shut up, you delusional pseudo-intellectual."