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1.
The result of a massive shit taken in one's pants, where the amount of poop is so much that it has nowhere to go but out the top. Typically happens to babies in diapers but it is also known to have occurred with fat, drunk bitches who can't get out of pants that are too tight in time to take a shit.
Person 1: What's all that brown stuff coming out of that chick's pants?

Person 2: I think she just back shat herself.
by The Hot Karl January 01, 2011