The State of relief and euphoia just after unleshing a giant crap(or perfoming "Shock and Awe") from your body... usually accompanied by a long sigh of relaxation as your sphincter retacts to its normal state. Much like the state of relaxation after an orgasm... kinda...
"I shitgasmed twicealready this morning... its gonna be a good day!"
the wonderful feeling of release caused by dumping a shit either so powerful or forced to be held in until the last possible moment ("the crowning"). Can be either a verb or noun.
He experienced the bliss of a shigasm in the gas station crapper after a 3 hour, Red Bull and french fry road trip