It's much more babyish and boffin, but funner to say and isn't illegal in schools.
It was made up by Drayton-Kids from West London.
Yes... Londoners are strange.
Jim: Oh bum-crumb!
Bob: Correct... Bum-crumb.
Usually left behind by an over-enthusiastic wiper.
(Often confused with Chuff Nuts which are bum crumbs that remain attached to the crack hair)
Ah fuck! Dave's left a load of bloody bum crumbs around the toilet again. That guy needs to stop wiping his arse like he's trying to polish his Rusty Sheriff's Badge. Dirty bastard!