Not parties, per se, but nude venues where open sexual contact was encouraged/permitted. I always only fucked the people I was with.
Except this ONE time. Very nice couple visiting from Estonia. I don't think I could do that again. I tried it, and though it was fun, I just ultimately don't want to fuck strangers.
I don't even want to fuck my friend's friends unless they become my friends too, FIRST. I want to personally know and evaluate my playmates. Most of the time, I could tell right away if I didn't want the friend of a friend to be in my sexual cipher. In those cases, I let him know they were off-limits to him too. These were usually women who demonstrated poor discernment while I was getting to know them. He always was disappointed, but he agreed to my terms. Fuck her if ya wanna, but then you can never fuck me again. He sometimes pressed me on this, letting me know that he would abide by my conditions, but that he disagreed with my decision. Then he saw my dire warnings about the wrecklessness of one of his friends come true. He told me about her troubles, and never questioned my judgement in such matters again.
But this one couple got through my filters. They were old friends of his, and I met them several times before we started hooking up. We never really swapped because I was not attracted to them. We just had sex with our own partners, together. Once, I gave the dude some head (with a condom, though that is not my usual practice) because sje wanted to blow my dude, had blown him in the past, and the couple swore she was so good I would learn new tricks. My dude had complimented her skills, but told the other guy that if I was ever willing to suck his dick, the blowjob would blow his mind. I decided to toss him one. But I missed something. Turns out, the wife was secretly going to adult theaters and book stores, and giving out a lot of random blowjons to strangers. The couple divorced over it. Dude said to me away from them that for all her enthusiasm and practice, she is really just okay, and that if not for how pretty she was, getting head from her would have been completely unremarkable. After that, I knew I'd never want to play with anyone I didn't know for myself.
But yes. I lounged by the pool naked, had drinks in the atrium naked, watched porn in the play spaces, warmed up in the sauna, all naked. Many wanted to fool around, but I generally stuck to the man who brought me, or the well-known group of friends we arrived with.
I did really enjoy watching others and being watched though.