It begins with a standard-issue turd forming in the colon from observing a normal healthy diet. Then, usually whilst drunk, you eat something which is known to have explosive diarrhea causing effects, e.g. Chipotle. This results in immense pressure buildup of diarrhea behind the turd "plug" in much the same way as magma builds up beneath a solid rock cap in a volcano prior to its eruption.
At some point you become acutely aware of this pressure and go scrambling for the toilet - if you're lucky, you make it in time. What happens next is in many respects similar to the discharging of a cannon or firearm. The immense pressure wave propels the solid turd out of your butt, usually splattering it against the side of the toilet bowl like a sticky, smelly artillery shell. The diarrhea then spews out in a manner not unlike the rocket exhaust of a space shuttle launch, coating toilet and buttcheeks with a soupy-yellow brown film.
Best case scenario is that cleanup requires a jug of bleach and a hot shower. Worst case, the hazmat team.