This phrase defines a flatulence that is of maximum horrid stench. A "Fart Nasty" fart can easily clear a room and make others gag in pure disgust. "Fart Nasty" is also one of the founding members of the "Fart Boys," who received the name from his constant revolting stench that emits when he passes gas.
(Loud Fart) "Oh man I can't breathe that Fart is Fart Nasty!!'
by Fart Boys December 10, 2009