Ive done it once with this chubby chick I used to date for a while.
She was a massive fiend for weird shit and we had just finished and she just says hey lets do anal.
I went from limp to rock hard in a second and I had to go really slow for her for about 2 mins before she said to just go as fast as you want.
Its very tight at the base but not painful and the insides are really warm and so soft, way more than the inside of a vagina is.
Was mind blowing awesome and I got a double orgasm from it were I came, there was about a 2 second downtime before I felt that rush of coming again.
We broke up because she wanted to do more weird shit and she went over the line with me.
Fucking bad decision on my part as I can never find another women to do anal.