A two bagger is a chick with a rockin' body, but a face that looks like it was beaten with an ugly stick. There are two principal reasons why someone would be called a two bagger. The most common reason is that a gentleman should be able to place one bag over her head and still enjoy the sexual experience, but for good measure will place another bag over his own head in case the aforementioned bag falls off the two bagger. Additionally, should a friend walk into the room while a sexual act with a two-bagger is occurring, the gentleman performing the act will be assured that his identity is protected.
Shawn: "Hey bud, you were a little drunk last night at the bar! If I was as drunk as you, I would have gone home with that butt ugly chick you were talking to! Did you put a bag over her head?"
Todd: "Bud, I would have used one bag, but she was definitely a two bagger."