When you are taking a rather large size shit and it gets sucked back up your butt which may feel like you are getting raped in the asshole.
One day i was sitting on the the toilet and i was taking a shit. This wasnt any old shit. This was a old,smelly,corny,crust,terrible shit. then suddenly, i couldnt push it out anymore and it came right back in. it felt like i was getting raped by my old jailmate bubba. He was black and had a 12 inch cock....around. The bad part was that he wasnt using lube.... and that is what a shitfuck is. for more info type in poopfrik