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1.
Someone who poops in anothers restroom and doesn't flush, or claim it.
Jarrod shat in the boat's crapper and left it to marinate all night. When no one fessed up to it, he anonomously became the "Mad Pooper".
by AdamnJenn August 28, 2005
 
2.
An individual, usually unknown, who defecates in improper places, especially when the discovery of the evidence is an unpleasant surprise.
"When Mr. Jenkins reached into his desk for the hall pass, he discovered that the Mad Pooper had struck again. The whole school heard the scream."
by MrClarke2014 April 14, 2014