Myself and a friend had some wacky times back in the day. We swung both ways, that was a secret it being the deep south in the 80's, and occasionally shared a wild young lady that he worked with. He got serious with another girl, they eventually got to having threesomes with the aforementioned wild young lady he worked with, and his girl eventually wanted to try being the center of attention.
She didn't want it to be me, thinking it might be awkward later so, unbeknownst to me, they put together a little soirée with the wild young lady and a guy my friend my worked with. I walked into a foursome that was really not going very well. The other guy was limp as a dishrag and having no luck at all. There was a great deal of frustration and tension and my walking in made it awkward, as it was my house, and my buddy was just staying with me while he got things in order to return to school.
Naked bodies everywhere, I was ready to go in a heartbeat. I proclaimed, "somebody is putting out, or everyone is getting out." I hit the floor with a girl on my face and a girl on my dick. Swapping back and forth, my buddy egging his girlfriend on. The other guy just sat and watched. It finally reached me banging her on the couch like I was on a mission while she tried to resuscitate my buddies limp willy while he encouraged both of us. He finally gave up and just sat and watched us go at it.
I am a Peter North kind of cummer and I just pasted her from her pussy to her forehead and she loved it. My buddy was out of commission so he declared the night over. I don't think his girlfriend wanted to end it, I know I wanted another go, but it was over. I was assured everything was cool and we would do it again sometime, but he broke up with her a week later and moved out. Didn't see or talk to him again for 25 years. I should have gone after the girlfriend, but the macho "guys don't do that stuff" got in the way. I ended up meeting the girl I would marry not long after anyway.
Sex is outstanding with my wife to be sure, but there is something to be said about conquering another guys significant other while he encourages it and others are watching mouths agape. My wife and I have had sex in front of others before and it was pretty fun as well.