A poass is a certain being who posseses both the qualities of being a poser and an asshole. This type of person is largely considered to be hostile to anyone around him and to act like a douchebag constantly even though he is clearly not one and is just trying to hard.
Non-Poass: Aw yeah, I just got a quarter.
Poass: I have 3 million dollars in my swiss bank account hidden in the Netherlands of the nile desert.
Non-Poass: That place doesn't even exist.
Poass: It does if I want it to! Im richer than you!