The guy who bites the bullet and drives to the party. The drunk driver has the critical role of getting his buddies home, or to donuts, or to more beer. It's usually customary to by the DD a beer for his efforts.
Its when you are having sex with some girl and you stick one (or many) of your fingers in the girls butt getting a little bit of poo residue on your fingers. You then put your fingers in the girls mouth resulting in her tasting her own poo. This then gives you the mental edge over the girl for the entire relationship because you know that she has already eaten her own poo.
I once gained "the edge" and now she doesn't want to talk to me.