1. When you're in the stalltaking a shit, and the sounds coming from your asshole are so foul and repulsive, that you are too embarrassed to come out of the stall and face the other people in the bathroom.
Joe: That guy sure has been in there a long time.
Lawson: He's taking a thundershit, he doesn't want to come out and have us see his face.
After eating 6 pieces of pizza plus 5 chicken wings at the pizza lunch buffet, Eric had to go back to the office and take a thundershit in the company bathroom stinking it up for so long that his co-workers could not use it for more than 35 minutes.
Another word for an epic Thunderstorm. Thundershitz are characterized by large, heavy, warm drops of rain accompanied by big BOOM BOOM BOOMs of thunder.