It's when a guy is banging someone in the butthole, they cum inside, then yank their cock out really fast, causing the butthole to pop out. After this, you milk the exposed butthole into a cup and make the other person drink it.
Susie ate tacos the other day..... when I gave her the butt cow, she threw up olives and lettuce everywhere, so I said "bitch, clean this shit!" I haven't given her the butt cow ever since
de E FeAzY 30 August 2007