Well. If you're gonna supply a drunken motorcade home for some obnoxious drunk bastards, you probably want a 'designated drunk' riding shotgun with you.
See, a 'designated drunk' can supply the obnoxious assclown you're picking up with all the drunken blabber that they can supply each other, leaving you free to drive in peace and harmony.
That way, he's not leaning in YOUR grill and blabbering stories about how cool high school was two decades ago as he blows moist clouds of Natural Light beer breath in your face.