Friend (and future room-mate) of mine wakes up one morning after a heavy night of drinking, looks down from his loft and sees a girl lying on her back on his couch, buck naked except for a pair of his jeans pulled up to her knees. He clears his throat and she wakes up and looks up at him.
Him: "Good Morning"
Her: "It's my Birthday"
Him: "Happy Birthday"
Her: "Thanks, (pause) where's ______"
Him: Laughs - I'll go get him.
She had broken parietals with a guy in the room two doors down, got up in the middle of the night to go to the bathroom - apparently naked - and went back to the wrong room.
The best part is, the other guy that lived in my friends room had to get up early that morning, but he was still totally blitzed from the night before. He gets down from the loft, goes and takes a shower, comes back and brushes his teeth and gets dressed and leaves. Meaning he was either too drunk to notice a naked girl on the couch, or she went on her little trip through the hallways after sun-up.