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A very runny poo. Usually caused after one eats many prunes or similar foods. A bum pee is liquidy but may contain other chunks of food (peanuts, corn etc)
"I hate bum pee" (Done best in a British accent)
or
"I had such a bad case of bum pee that the toilet looked like it was full of ice tea when it was all done"
by SpMaAl October 22, 2008
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