Peter, having taken too much "liquid courage" in order to talk to Mary Jane at his Aunt's wedding, accidentally wound having sex with his equally drunk roommate, Michelle. Thanks to an alcohol-induced blackout, he had no memory of the night before (and even initially thought Michelle was MJ at first when he woke up to see a naked woman sleeping next to him). When Peter expressed surprise and confusion, Michelle realized he didn't remember their drunken tryst, and she kicked him out of the apartment. And if you think that sounds bad, it is.