A shart that is so powerful in nature that it contains the properties of a shotgun blast. When a mega shart occurs, the 'victim' will usually feel horrible for about 3 hours leading up to the blast. When the time comes, the person will usually get on their knees as a result of the pain; the mega shart usually occurs about this time, blasting out of ones asshole, usually tearing muscles and distending the anus, the blast blowing out of the pants in a shotgun like manner.
Jim was gripped by pain, and, being the experienced man he was, he knew it was a mega shart. Falling to his knees, he let loose, feeling the extreme pain and massive amount of crap rip through his ass, and burst out his pants.