Used to describe the need to relieve your bowels after a night out. Mainly used when you wish to state this in public places but wish to remain polite.
Has a rather large usage in the Cavan-Sligo-Leitrim area of Ireland and is quickly catching on. Nobody is sure where this term originated from but most suspect it is the Cavan area.
Ahhhhh crap.....I need to BP NOW!