An upholstered couch, settee, or other form of seating, which has been saturated with flatulence to the point that its foam interior permanently reeks and may well have acquired a brownish tint.
I don't mind watching the football game at Joe's house, but there's no way I'm crashing on that fart sofa after everyone's had chili dogs.

On "My Strange Addiction", I saw a woman who eats bits of foam cushion from used couches — can you believe she actually snacks on fart sofa?
by FlatusMeister August 21, 2011
Get the fart sofa mug.