Now that you mentioned it, my first contact with electronic adult content was in the 2600.
One night I was having trouble sleeping, and came down from the stairs to the living room.
My father and mother were on the 2600. I could not figure out what they were playing on the screen, but my mother was laughing.
My father said it was the "x-men", it was a adult game, but I was a child so I didnt understand the elements on the screen. He had rented the cartridge.
My mother chastised him for letting me see it, and I got back to bed.