An attitude whereby a person pretends to like a band they don't really like. It is a public view. In private, they'll listen to Abba and Air Supply but would never, ever admit this.
The rich people in Chekhov's stories often pretended to be infatuated with the arts. This idea is my strongest impression of what it means to be pretentious. It implies that a real love of or understanding of the arts is not at all pretentious.
People sometimes are not content with the results of being "the real me," so they reinvent themselves to try and get more dates. Hey, if it's about getting more dates, wouldn't you?
Deep down I guess it could mean that the dude really loves a weird-looking unpopular chick who listens to Air Supply, and though she's smiled at him before, he rejects the idea of lowering himself to her standard because it might affect his "rep." He never asks her out, never gets that one booty that really was meant for him, and wanders aimlessly among other cool people.
So hopefully, pretentiousness is a phase one passes through in the socialization process. Where it becomes chronic, possibly the pretentious persons themselves are the ones harmed the most.
Too bad I overlooked that quiet girl I really liked and wasted my time chasing hot chicks way out of my league. Man, was that pretentious.