Anal dildo (guy)

Well, a lot of women have a clitoral orgasm during anal sex because they pleasure their clit while the back door penetration is going on. A man having an anal orgasm (I've had MANY) might be similar in that the cock and clit are pretty much the same sexual member. If you're jerking as you cum then it might be close to the women's clit/anal situation.

On the rarer occasion that you can cum from anal sex just by stimulating and massaging the prostate, I'd look at that as more of the female occurrence of a g-spot internal based orgasm. I can't tell you what that feels like because an anal orgasm from just anal penetration and massaging has never happened to me. I get close, but just like so many women that have never had a g-spot orgasm, it's never came full circle.