Similar to projectile vomit, except from the anus. Normally explosive diarrhea is bile and orange juice, accompanied by chunks of scratchy objects ranging in size from a pebble to however big your ass can stretch, and unexpected volumes of fart which do a marvelous job of dispersing said liquid and chunks. Explosive diarrhea is deceptive; leaving the top of the lid virtually unharmed, yet devastating the underside.
A diarrhea so explosive that you can hear a guy with explosive diarrhea scream, smell something foul, and see pure shit coming out of a stall and a guy flying and bursting through the roof or the porta-potty flying with him as he lifts off the toilet seat. Then, his ass ejects millions of nukes while he is falling down and detonating them and probably killing you.
When you're sitting on the pot and you've got diarrhea and you blast a dukie SO hard that it explodes out of your butt, leaving your toilet in ruins, and you with a bloody ass.