In the real world, the term 'Hipster' is meant to describe someone who says or does things different from the majority for no other reason than for the sake of being different (or "hip", hence the term "hipster.")
But the way I hear the word often used (especially in the world of the interweb), it's usually intended to describe someone who dares to disagree with the majority on something (either on a specific forum, or with society in general) and thus getting branded the negative term "hipster" for doing so, because fuck forbid somebody actually likes something or arrives to a conclusion on something that happens to differ from the majority, right? In this context, the term is typically just an easy and convenient way to dismiss someone's feelings or arguments on something without having to actually engage them in why they feel or see something a particular way. Accusing someone of being a "troll" (and thus, allowing you to justify dismissing them right out of hand) for taking the opposite view of whatever the consensus is on a particular topic works in a similar way.
I mean, after all, if history has shown us anything, it's that the majority is always right, eh? (I'm being snarky, of course - history has often shown us just the opposite.)