This is a great question, with so many possible answers, but since the question pretty much asks for one thats what I will give.
So as a reference I am a pre-op transexual woman. A couple of years ago I was in a relationship with a guy who had the biggest sexual appetite I have ever come across in a partner. The things we did in those twelve months still turn me on. But the hottest for me has to be the first time we had a threesome. He had invited one of his friends around for an Ice (meth) session and we just smoked and talked for hours. Eventually, as is often the case, talk turned to sex.(Now my man was always ready to go, but the hormones Im on means my libido tends to be somewhat diminished, I loved him however and was always willing to please him. When I am high however, I am insatiable myself.) So we're talking about things we've done in the bedroom, partners we've had that sort of thing and I still dont remember exactly how it came about but all of a sudden I've got my mans dick in my mouth while the two guys are still chatting away.
At that point I was so fucking horny I would have sucked his cock in the city centre, regardless of who was watching. A few minutes of this and some dirty talk from the guys and my man asks if I'm up for a threesome. I pulled off of him long enough to moan god yes before getting back to work. And away we went, this was a marathon sex session that went for many hours, I was fucked in pretty much everyway I knew about and a couple I didnt. But one thing stands out as the hottest experience I have ever had.
The whole time we're fucking the pipe is still making the odd appearance. At one stage Im riding the other guy cowgirl and sucking on my man, he stops for a bit loads up a pipe gets it rolling and then gives it to me while Im still riding his friend, I blast away get a good hit and go back to concentrating on the cock in my ass whilst my man sits on the couch behind us to have a blast and watch for a minute.
Next thing I know he is behind me and kissing his way down my back telling me how hot this whole thing is. Then he whispers in my ear, if at any time you want this to stop baby just tell me. Then I feel his lubed up fingers pressing at my ass which is currently full of his friends cock. Im moaning away as he continues to try and open me up some more. And then it happened, he pushed me forward and got in behind me and slowly work his cock into my ass as well. I cant say that at first it was the most comfortable thing in the world, but I have some bigger toys and dont mind a bit of width. It didnt take that long to adjust though, and I couldnt believe it, it was the kinkiest thing I had ever done in my life and the thought alone was blowing my mind. It was a little tough for the guys at first, trying to get positioned right and work out their rythem. But after that away we went, they fucked me like that for at least an hour, occasionally swapping positions themselves, or turning me around or pulling out for a quick suck. I came 3 times with them both inside me, twice without even having to touch myself. I lost count of how many times they came between them but I know they outdid me over the hours we were at it.
Getting fucked by two guys at the same time is still the hottest thing I have ever done in the bedroom. Ive been lucky enough to have a few more similar experiences since and have loved them all. My man and I broke up about a year later, we are still friends though and if it ever comes about that we are both single at the same time we dont hesitate to get high and remember old times, if you know what I mean.
Sorry about the long post, this is a drug forum.......what do you expect!