A tremendous expulsion of gas coming from deep within one's loins often resulting in liftoff into the upper atmosphere leaving a trail similar to the of a comet
"Bro, my man just absolutely comet farted."
"Bro, I can't believe he would comet fart in front of his future father-in-law"
A release of a stink that makes (a) you almost feel like you are lifting off, (b) you want to get out of the room, (c) others who experience this mighty flatulence need to evacuate, hence flyaway and fast.
Boy, oh boy, Bruce, let one of those flyaway farts fly at work today, and the whole office suddenly went on a coffee break in the cafe!