I think it's originally a chatroom thing. And being a girl myself, I know which types of girls do that. Usually the girly girls (I love boys, I love makeup, I love shopping types), or 12 yr old teenyboppers who have no sexual experience at all but are fascinated with it. I don't think many girls really get what they're putting out there when they choose usernames and think it'll be cool. But it's really not. It's totally lame.