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When one person is seated on the toilet and another person sits on that person's lap and craps through the first person's legs. Usually occurs in dorm rooms housing excessive occupants and there's only one toilet.
"Open up your legs" Cassie pleaded. "I really have to go"!

Scott objected, stating "I do not engage in crap stacking!"
by Pfc. Snowball July 19, 2008