A trail of clothing leading toward an area where sex is taking place. Usually a bedroom, a couch, a cave, where ever two or maybe three, four or five go to get their freak on.
Room Mate #1: Hey Dude, what's all this clothing doing on our floor?
Room Mate #2: It's a sex trail leading to Ryan's room.
Room Mate #1: He must be getting a mouth full up there, look at this bra, 36 MM
Room Mate #2: Yeah, he's a motor boating son of a bitch!