When you take care of your friends who have had far too much to drink. This goes above and beyond the simple task of being the designated driver as it includes but is not limited to:
Making sure they don't get into fights
Making sure if they do get into a fight, damage received is minimal, while damage inflicted is maximal.
Taking lots of pictures while they're throwing up in random places
Brositting Mike was hard enough, but then when Chris had too much to drink it almost got out of control.