Cotton panties or underwear that have been farted in so many times that the fabric near the anus becomes partially transparent to the point where the spot is distinctive.

Sunderwear is never shit stained nor is it created by direct contact with poo matter. Rather it is created by the various chemicals in the fart acting upon the underwear fabric.
he sure does, i bet he has a whole drawer filled with sunderwear.
by flapjack27 December 8, 2010
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