This happens when you are in the middle of trying to silently pass a fart, but suddenly your asshole shifts in just such a way that you know that if you continue passing it wil come out loud as a bugel. You then sit there attempting to pass it silently, which causes your face to contort and you to stop breathing in an effort to make sure no noise comes out.
Friend 1: "dude, i was talking to this hot girl last night at the bar and i tried to pass one but i stopped 'cause i knew if i passed more it would sound like a nuke."

Friend 2: "dude, you totally went into fart purgatory."
by tetris57 November 9, 2011
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