Brian: You don't need to put your P in a V right now.
Peter Bretter: No, I need to B my L on someone's T's.
When the guy walks in on Peter naked in bed, the sheet protecting Peter's modesty is covering him in one frame, and the next moment it has vanished completely.
A some details are taken from Jason Segel's life. For example, the naked breakup is based on a similar incident and he was working on a puppet-based Dracula rock-opera.