Accidentally shitting yourself when trying to force a fart.Many times a situation just call for a fart-as a comic relief or just because someone's face happens to be in the vicinity of your ass.Forcing a fart with an underlying,but asymptomatic case of diarrhea,will almost certainly result in a scataclysm.
Mom handerd me the phone and said,"Here,wish your grandmahappy birthday." So,I place the receiver near my bung and tried to ad lib a fart resulting in a scataclysm.
A catalyst for shitting. Any product that, when consumed, will cause a rapid onset of bowel movements.
Jorge poured rancid beef juice into Simone's beverage, well aware that it was a shatalyst; he wanted things to get kinky that night.
or
Kevin: Have you tried the new burrito place on 5th?
Reginald: Yeah, they're jumbo burger was a shatalyst. I painted a mural of a sandstorm on their bathroom floor, if you know what I mean.