I have a bottom friend who once told me he thought he would like to get fucked by two cocks at the same time. Well we haven't been able to make that happen yet but one time while I was fucking him from behind I slid a smooth vibrator about the same size as my cock inside him under my cock.
OMG! That vibrator on my cock inside his tight ass felt so good!
I have done this before in a pussy but never in an ass. I didn't last very long because the whole thing was just so hot and felt so good to me. I don't think he enjoyed it as much as I did but he didn't complain. I said, you wanted to know how two cocks would feel.....