Quite simply, bumboclaat means toilet paper. Bumbo means bottom, claat is the Jamaican pronounciation of cloth. Very mild swear word, but in Jamaica, where swearing is a very serious thing, a few 'rebels' managed to get away with bumboclaat...and it caught on.
Used for emphasis or exclamation mainly:
Dat bumboclaat policebwoy arrest mi fi nutt'n!
A weh di bumboclaat wrong wid yuh?
Bumboclaat, she have a big bloodclaat batty