Flatulence released from the anal cavity, which is powerful enough to project fecal matter at dangerous velocity onto the flatulator's undergarments. A strong wet fart. Otherwise know as a shart, these noisy explosions tend to have a distinct "quack" sound when released past the sphincter.
(ex 1) Shit ran down my thigh as a result of a disastrous quack.
(ex 2) Tony accidentally quacked while trying to light his fart, in this situation a basic joke had become oh so dangerous.