When you try to squeeze out a fart with great force but you end up shating yourself, usually catastrophically.
EX:
Dude, I had gas last night after dinner with Ashley and I ended up poo poo farting on my way home in the car, The dry cleaners had a hard time cleaning that shit.
A fart that does not sound normal because it is blocked by poo. As a result this fart will also smell much worse because it has to travel past the poo to escape, picking up the stench on the way out.
eeewww!!! Gross go to the bathroom you know that was a poo fart.