I've have my vagina fisted by men and women, maybe four times. It does nothing for me except make me sore, and pee uncontrollably.
I girlfriend and I were into some heavy anal play, and she got her fist in my ass first try. Before even moving it around I had an orgasm that shook my whole body. I lay with my face in the pillow, and don't remember her taking her hand out. I was on another planet.
We did it again some time later. I came again as soon as her knuckles popped in. This time I maintained my composure, and she started moving it around. First rotating, then making little strokes. She pulled back to her knuckles a few times, which was heavenly.
On our third time, instead of balling her hand into a fist once inside, she carried on further up, and paused by the entrance to my colon. I could feel it opening up, and welcoming her hand.
I've done it with a man, but his bigger hand goes in, but I can't let him move around much. I still come like crazy.