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The substance or stain left in ones underwear when a fart is mixed with diarrhea.
The buttoxin in your underwear just won't come out.
by Roland Warren October 30, 2006
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When a person releases a particulary nasty smelling fart into the room.

a fart which is released from the buttocks, which could be described as being toxic.

hence the name buttoxin.

Butt + toxin/toxic = buttoxin.
Jim: *loud fart*

Jenny: "eugh, that smells disgusting!"

Jack: "that's toxic man."

Jim: "that's a true buttoxin!"

Jenny: "so nincompadrae!!"
by ClareyMcfarey :) March 02, 2010
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Ah, that fart was Buttoxic

Damn, that Buttoxin is gonna kill some one

Caution, bathroom closed due to a spill of Buttoxin
by pairofpant January 18, 2010
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