We had a hot tub and had backyard bbq gatherings.
There were 2 couples and us, if it was just us 3 couples the girls would go topless, no sex play ever happened but it was fun for all of us.
We had an older couple we were friends with, they were older early 60s, we were 45 at the time. Our home/hot tub or theirs we'd go naked. They were very fit and good looking even when naked. At our place we were only naked in the hot tub, at theirs we'd be naked in the hot tub, stay naked in patio chairs in the back yard and in and out if the house, kitchen mainly. Hot tubs, hot weather...hanging balls. Once in their kitchen he got a semi chubby, that got me full hard. It was embarrassing but no one said anything. Kinda awkward standing there with a growing dick and nowhere to hide. It went down pretty quick.
I remember his balls and how low they hung, mine did too I'm sure.