A bruise or gash that you wake up with after a night of partying or heavy drinking, with no remembrance of what happened or how you got it. Occuring with the stupidity and clumsiness of intoxication.
Mike - "Woah Dude! That bruise is huge, what the hell happened?"
John - "Drunk Bump"
Mike- "that explains it.. you were REALLY shitfaced last night"