A phrase commonly used by hipsters to indicate that they want to lean against (or 'post up') against a wall, preferably brick, to smoke a cigarette or drink a can of Pabst Blue Ribbon. Hipsters are led to believe that this is the cool thing to do. If there's no cigarette in hand, some hipsters replace the void with a can of PBR, the well known hipster beer. If they have nothing in hand, they fail at properly being a hipster. Generally, if caught in this scene, the hipsters would lift one leg up and rest the sole of their shoe against the side of the wall, completing their "cool" appearance. When suggested to 'post up,' a fellow hipster knows exactly what he/she is talking about and will usually agree to. It's the hipster thing to do.
Victor: Hey man, let's post up.
RJ: Alright man, let me grab my cigarettes.
Allen: Guys, I quit smoking.
Victor: Don't worry about it man, you can still post up with this can of PBR.