The first time I did vaginal DP? Well, yeah I did things with him. I ate his wife to climax while he watched. I fucked her for a while, then we got into position with me under her and she straddled me. He got into position between both our legs, and eased in on top of my cock. Bare skin on bare skin for all three of us. I was a little nervous thinking about his cock squeezed against mine by her pussy - the "label thing", and all that - and it hurt a bit until he found the location, and angle, that let him push in. She was rather uncomfortable too, and afterwards admitted that she thought more about my cock tight against his cock, than about the idea of having two cocks inside her. He did most of the moving (I was on the bottom, squished beneath both of them) and could feel his cock sliding back and forth against mine. It felt good, an unusual sensation in the physical dimension but a little unsettling to think that another man's cock was stimulating me and making me feel so good. He didn't last long. I could tell he was about to cum because his strokes got a little irregular and erratic. He pushed deep, and I felt the warmth suddenly flood over my erection as he squirted. "Instant silky seconds" - only more intense. I felt his cock jerking and twitching against mine, and my own orgasm hit me without warning.
Afterward was a little awkward because both of us guys - him more than me - were self-conscious about being stimulated to orgasm by another guy's erection. I played with that couple irregularly for a couple of years, and did vaginal DP one or two other times with them, mostly at her suggestion. I also liked to be under her, eating her pussy in a up/down 69, while he fucked her doggy style. In that position you can't do a good job of stimulating her without also stimulating him, and I tried to do a VERY good job of stimulating her. He, however, made an effort to minimize contact between me and his genitals. He and I never sucked cocks or fucked ass on each other.