backfire
The moment where, when you're taking a shit, a large pocket of gas (referred to as a future-fart) that was resting mid-shit or between two shits escapes as you're passing your lovelog, resulting in a sudden violent fart than not only propels your previously freefalling turd at Mach 2 speeds, but also results in a pleasing shotgun blast of turdlings across the toilet bowl.

A backfire is so named for it's similarity to a car backfiring.
"Man, I was taking a dump and backfired, and now I get 'Nam flashbacks when I visit the shitter."