This actually happened several years ago.  My wife was from Europe, so every year she would take the kids back to visit her parents.  One time while she was gone, I went to San Francisco to see a play and afterwards stopped at a small bar for a drink.  I was just about to leave when a drop-dead gorgeous girl came over and said, "Hi. you seem to be alone.  My husband and I were wondering if you'd like to join us for a drink."  Of course, my first thought was that she was a hooker.  But what the hell - having a drink with them would be harmless.  So I followed her over to their table.  Her husband was incredibly good looking - maybe 30 years old - about six feet tall and slim but with an athletic build.

I sat down with them and we hit it off immediately.  Derek was an intern at a local hospital and his wife Kathy was an English major, but was working as a go-go dancer to help support them.  We talked for almost an hour, and had fun laughing about some of the people around us and the silliness of the human animal in general.  Finally, I excused myself to go to the men's room.  He followed, and after the door closed he said, "I don't want to scare you off, but Kathy and I are both bi.  If you're interested, we'd very much like for you to come home with us and play."  I was half hard already, but that brought my dick to full attention.  With great difficulty I managed to pee and then we went back to the table.

We left the bar and found we were parked close to each other.  Derek said I could follow them, but in case we got separated he also gave me their address.  It was a small apartment in the Haight-Ashbury district.  I followed them with no problem and we went inside.

Kathy fixed tea for us.  We sat on the living room sofa and talked some more.  I was in the middle with Derek on my right and Kathy on my left.  The sofa was small, so our bodies were touching and I could feel their heat through the thin fabric of my shirt.  I glanced down and could see the outline of Derek's hard cock through his pants.  Needless to say, I was also hard and sticky.  Soon Derek said, "let's go into the bedroom."

The three of us stood together by the bed, and Kathy said, "Why don't you and Derek undress each other.  He likes that."  So we took turns taking off each others clothes.  When we got down to our jockey shorts, you could see the outline of our rock hard cocks with a wet spot at the end.  I slowly pulled down his shorts and as his cock appeared I saw he was uncut.  The foreskin made a little well that was filled with precum and overflowing.  I dropped to my knees, pushed the foreskin back with my lips and ran my tongue around the head a few times.  Derek shut his eyes and moaned softly.  I stood up and he took off my shorts.  He slowly took my cock in his mouth and played with his tongue on the head.  I just about went nuts and had to work hard to keep from cumming. 

After a few minutes he stood up and both of us undressed Kathy.  She was as beautiful naked as I had imagined.  Nice full breasts, slim waist, beautiful auburn bush around her pussy.  She was obviously turned on.  There was a thin white line of lubrication covering her slit, and the inner lips were swollen and pushing out.

Derek and I both dropped to our knees and started slowly licking around her slit and over her swollen clit.  She closed her eyes, tilted her head back and sighed.  After a few minutes she softly said, "fuck me."  So we all got on the bed. She laid back with her legs spread wide apart.  Derek lowered himself over her and I guided his cock to her slit.  He slowly entered her.  Both of them sighed and moaned softly.  As he slid in and out, I leaned over and licked her clit and gently played with his balls.  He pulled out and I sucked his cock for a few seconds then guided him back in.  She came twice, and finally he could hold back no longer.  "Oh fuck, I'm gonna cum!" he said.  He sank his cock all the way into her and started jerking and moaning.  Both of them were dripping wet with sweat.

After a minute or two he rolled off her.  She turned to me and said, "now I want to feel you in me."  So I took his place.  He gently rubbed the head of my cock along her slit a few times and then I slid in.  It was incredibly slick from his cum and her juices.  We slowly fucked while he played with my balls and licked my cock on the out stroke.  It didn't take long until my whole body tensed and I knew I was about to cum. Derek saw that and said, "pull out - I want to taste your cum."  So I pulled out and he quickly took my cock in his mouth.  I immediately went off with a mind shattering orgasm  He ran his tongue around the head while I was still cumming and super sensitive.  I really thought I would go nuts.  Finally, as we all cooled off we put our arms around each other and agreed we should do this more often. 

They called a couple of times after my wife returned, but I wasn't able to meet them so we never saw each other again.  But I have to say, that was the hottest sex I've ever had.