my kids dad tried doing it to me there's just no way. it friggin' hurt. even after having a baby he couldn't get past just his fingers. i don't understand at all some of the clips i see how they can even do it, their bones must be a mile apart.
in college there was a 15 year old girl i used to hang out with, she worked in the cafeteria and one of my guy friends like her so i tried to hook them up. turns out she was gay and ended up telling me one day that she had a really big pussy and liked being fisted. That blows the stretched out theory but i still think it has something to do with how close your bones are together. she used to stay overnight with me in my dorm and everyone thought we did stuff but we never did.
i'll experiment if my guy is curious about stuff but i don't see the appeal of fisting, it just isn't sexy at all.