Into the beginning of the movie, David walks into the old lady's apartment where they invite him for a game. Later, the red head sees him his socks and raises his shorts. As he steps out of their apartment, he is minus the shorts, but still has his socks. Hmmm... also, he apparently left his mail with the ladies.
Maybe he put his mail in those bags he is covering his wee-wee, but this brings up another point, where did he get those bags from??? he never carried them into the womans apartment