What is Fart Muffler?
1.
The act of holding toilette paper over the rectum while passing gas in a public restroom stall in order to conceal the noise of flatulating.
Because the ladies room was full, Erin used a fart muffler to conceal her true intentions in the stall.
See
2.
an acronym for ass or butt or booty
dude, keep your fart muffler out of my face