I can't think of an actual (having) sex moment, but I have a sexy one.
For quite a while I had wanted to photograph my wife nude having a shower under a beach shower (outdoor shower just off the sand at the beach). I had selected a beach, but it was quite a busy beach, but when the sun shone on the water, the background was magic, so I REALLY wanted this particular one. We decided to try it just after sunrise. We went down there about 20 different mornings, but it was just too busy.
Then one morning, it looked like the rain that had fallen for the last several days, would stop. We headed on down, and sure enough there were only a couple of handfulls of people around. My wife got ready, I had to run along a path to make sure no one was coming from two different directions, and check on a nearby carpark that fishermen used. Finally, no one was around, so I said "let's do it". She dropped her dress, turned the shower on and started posing. I had taken just 3 or 4 shots when she started waving furiously at me, calling out my name. By the time I put my camera down and started walking towards her (I was in a rock outcrop) I saw the 3 fishermen walking around the corner, about 2 feet from her with eyes popping out! One guy just casually said "don't worry love, if I had your body I would show it off too"! They just weren't there when I checked....
We got back in the car and even though I am a professional photographer, I discovered that I was so excited to be finally doing it, I had forgotten to put film in the camera! This was 1999. My wife assured me we were not doing a repeat performance!
I made my own "mock" beach shower, and took it to a more deserted beach where we spent several hours getting many great shots. Some of these shots have been blown up to poster size and are on the wall of my studio office (private!).