A term used to reference people who are being pansies and should just suck it up and go for it, usually in the case of a member of the opposite sex that they are too shy to approach. From "Harold and Kumar".
Kumar: Dude, there she is, you should go talk to her.
Harold: No, I'm not going to just go talk to her.
Kumar: DUDE! Don't be a Vagina McVaginestein!