Where shit drys in your ass after its been improperly wiped and when you scratch your ass it falls out like dust and it gets all over the place.
you fuckin arse you left bum crumble all over th toilet seat.
To administer a royal bumming...To open a can of whoopass on one's friend/nemesis/child...To give someone a jolly good thrashing at something, e.g. a computer game, or contact sport such as killing.
"You'd better not be trying to overtake me adey. I am the king of rollcage and I shall be making bum crumble if you aren't careful. you assmunch."
"Put that child down adey, you can't bring him with you or you'll get a fresh serving of bum crumble from that police officer"