1)when you take a dump and it's impossible to get out. when it finally does, you sigh in sweet relief and step off the bog to admire your big brown baby. when you get a good look at it, you realize that it is much bigger than you thought and pat yourself on the back for getting it out the poop chute. you get an even CLOSER look, and see it is not merely one big shit, but rather TONS OF TINY SHITS IN A CLUSTER! FUCKIN AWESOME!!
2)what one calls one who has achieved a minor level of douchebaggery. a weak cuss word of sorts. can also be when you pop one out and it is HUGE, i.e. a nugget of brown gold.
bumnugget can be used from a whore who has achieved the ultimate level of douchebaggery by skanking around he who has dick, to old man who drives shitty toyota and doesn't move his car through the light until only he can get through. it is applicable anywhere.