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
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.
"Base we've got some square groupers floating outside of Miami harbor."