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The jet of urine which bouces back from the toilet bowl and up to the nether regions of the toilet-sitter, caused by expulsion of a urine stream with excessive volume or force.
Jane: "After those two pitchers of pabst I peed so hard I undersprayed."

Jill: "You're an alcoholic. And you smell like urine."
by Nerdiva March 28, 2011
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