Main Principle: There is no such thing as a self-identifying hipster.
To be a hipster is to not genuinely "try" to be anything. All personal tastes, specifically fashion and music, involve irony and a level of mockery. Thus, to admit that you are a hipster means that you're legitimately trying to attain a certain image, and you are therefore not a hipster.
Corollary: You can't pretend to be a hipster, because pretending to be a hipster implies that you are ironically mocking them, and thus, means you are acting like a hipster.