A hard ball shaped turd that fires out of the anus at a considerable speed when pushed out of bum crack making a similar sound of a pebble being thrown into a lake.
Oh no!! I just dropped a seriously big bumnut and have just experienced a splash back on the arse hole!!
A piece of harded exrement, that clings to the hair around ones anus. Some bumnuts cling to the hair so well that removing them can rip the hair out from the root which can be painful.