1: An expulsion of air released by the penis.
2: A reference to someone that will never make it in the real world, or is too much of a pussy to get shit done. This originates from the fact that "penisfarts" never happen.
Tice: Yo whats up with Morgan? He's been failing all his tests and he never goes out anymore.
Dylan: Yeah I heard he's been a real penisfart recently. He needs to step his game up.
Tice: True, true.