I was the first to propose C, and I have to confess that I am guilty of the offense myself. However, it was well after midnight, and a very long way from any others gathered at that beach, at least a quarter mile. Our fire attracted a visitor, but we could hear him coming and my wife just wrapped herself in the blanket and I sat naked on a log in a position that he would not be able to tell that I was nude. We spent the entire night on that beach and did not get dressed until the sun came up. So, I guess there is room for all three answers if the circumstances are right.
My initial inclination would be to ignore and move on but as a few have pointed out this type of behavior can and does lead to clothing optional beaches being shut down. My beach is Gunnison on Sandy Hook in New Jersey and The National Park Service would not tolerate behavior of this sort. Higbee Beach on the southern tip of Cape May further south of Gunnison used to allow nude sunbathing but no longer does at least in part because of overt sexual activity. My vote would have to be option B because I want to keep Gunnison as is for as long as possible. Which also means no glass containers and take your trash out with you!
Honestly, all depends on level of privacy they expect/wish.
If it is at present empty, but a place where logically and often patrons of the nude beach roam around, even if not part of the beach, it is not really I thing I would endorse, even if I would not report it either - and myself, I enjoy sex in the outdoors a lot.
It is a very thin red line, when a place is private and when it is just empty of people for the moment, and the chance of being spotted by people who would not fancy the sight is high. I accept people do get their kicks of the possibility of "getting caught", but they should avoid nude beaches and immediate environment for such activities, alone for the reason that it bring a bad name on the activity and again would attract more jerk-offs, exhibitionists, voyeurs rather than TrueNudists.
Chances are it would be a normal women that had to be talked into doing it. My inner child say's to loudly cheer and coach them, HEY any body else want a piece of this action ;-) The average women would probably kick him away and never let it happen again ;-) But there are some that this would only add fuel to the fire, I suppose :-(
And yes my inner child needs a lot of adult supervision. Or like a bumper sticker I saw , "WARNING My inner child is a mean little bastard" ;-)
If I was hot and heavy over someone and had an opportunity like that in the textile world and went for it there, then I assume Id do the same thing being nude assuming we thought we were being discreet and thought we wouldnt be seen. Im thinking the fact it was a nude place shouldnt matter, but as others have stated, the authorities would obviously claim it was due to the nudity and if it was happening often enough it would get shut down. But not in the textile world, it would just be more policing of the area.