Staring? That would be weird. Looking, talking about the display, maybe paying a compliment if it’s genuine, that’s been my experience.

That’s assuming a new couple. Most of the time, when it’s regular thing, I ceased to notice the nudity at all, but I was used to group scenes and casual nudity in general. I would be more curious about new partners, obviously; but when I was part of a couple’s swap (you don’t have to be married to play) it was mostly with established friends in the community. Totally new couples would tend to be less new as well, since the typical start to a fresh swap was at a meeting or party of some kind related to kink, group sex, etc. I would have seen them naked most likely, if not had sex.

Since that was how I had been introduced to swapping in the first place, I think I may be a bad example of what you’re asking.