when the gluteus maximus expands in such a manner where your pants become undone, or the associated breakage of the lower garment fastening device due to ass expansion.
had to buy new pants today when i butt gusted the button into two pieces.
by gabmab October 22, 2013
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A. When you laugh so hard you fart.

B. When a fart sounds extremely funny.
I had a good Butt Gusting laugh after I let out a squeaker.
by Jason Henderson Amare April 20, 2013
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