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2.
Another name for bad diarrhea. Especially if there is a lot of it and it comes out with a lot of force, causing you to bend over and strain a lot, almost like you are dry-heaving or about to barf. But you do it out your butt instead of your mouth. Butt barfing.
Man, what is up? I heard you in the bathroom and it sounded like a waterfall in the toilet?

Uhhhhh, sorry dude... I had major butt barf. Might not want to go in there for a while.
by offya December 21, 2011
 
1.
a watery, chunky substance that is excreted from the anus in violent bursts
That mexican food gave me a wicked case of butt barf.
by Feason April 29, 2006