BP
abbreviation for butt piss (chronic diarrhea that literally shoots from the rear in liquid form). In Oregon trail days it would have been a prime indicator of the onslaught of dysentary.  Often accompanied by machine gun like fart sequences. Also occurs when subjected to an extremely low carb diet.  Food (or remnants of it) may be semi-identifiable when the process is completed.  If ignored, may result in a hardcore shart.
I'm going to have to refrain from Long John Silver's tonight because I really don't want to have a BP attack while we're at the bar.

I'm sorry but I really need you to cover for me before this BP transitions into a shart.