you try and remember "your lines"

plus there is sometimes doubles on the body closeups

The current trend with some mainstream "hot" movies is that the actors actually have sex, although I think that trend has cooled off recently

He was doing a rather hot under the sheets scene with an actress

Just before the cameras rolled, he said to her, "Whichever happens, I apologize."

That's one way to make the best of an uncomfortable situation.

some will tell you it's not as much fun with all the crew there but others will openly admit that they sometimes enjoy the scene. I'm leaning toward the group that feels offended if someone doesn't get worked up about it.