Sound wise a "penis fart" can resemble a queef or the sound a hose makes when extra air escapes.
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.
Dylan: Yeah I heard he's been a real penisfart recently. He needs to step his game up.
Tice: True, true.
'Dude, she made the titanic look small, that was such a penis fart'
'Why is it everytime I go to Mooseheads bar I wind up having a penis fart?'