Back around 1980 me and my college GF would go to the drive in. Wasn't X rated but some pretty hard core R rated. Always had steamed up windows and some good fun. Later we went to an adult,theater in the next town over. Old school flicks with the likes of Ron Jeremy or John Holmes. Didn't really do much for her.
My wife and I enjoyed many episodes of "near sex" at drive-ins, but never actually had sex. I recently learned that she and one of her college lovers did have sex at the drive-in on a night when it was raining so hard that they couldn't see the screen and the security guys weren't wandering around among the cars.
Don't know about today, but in the past Youth Guidance Officers would park in the last row and use binoculars to look for heads in the cars in front of them. If no heads, or only one head, visible they would move in and let the steam out of the car.
At our drive-in, the security guy kept a close watch on the last row. Some of my friends parked on the front row because the security guy never went there.