A bowl movement, jobbie, or crap session of such intensity that it is measured to the power of one million standard craps. Such is the magnitude and intensity of a mega grunty that it can be beyind the capability of the average colorectal system and therefore a mega grunty may need to be delivered by cesarean section. A mega gruntie can be both intense and satisfying and can therefore result in a backdoorgasm.
"Sorry to take so long, I was almost torn in half at the seams by a massivemega gruntie!"