Usually this happens when you can't make it to the bathroom in time and the poopie makes in your pants, this is squished into a ball and when you take your underwear off it hangs down and looks like a sack-a-poopie.
Matt ate a lot of beans and now he has a sack-a-poopie

Matt likes to have sack-a-poopie for lunch.
by Josh Whitmarsh March 25, 2006
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