Back in '90, a friend of mine showed me a game he had gotten off a BB for his Commodore 64 (actually, a friend of his got it for him, because none of uu could afford a modem). It was a German game called "Party Girls".
After starting the game by typing Load "PartyG",8,1 you were presented with a digitized screen capture from a porno, rendered in full 320 × 200, 16 colors glory. Pressing the button on the joystick took you to a screen on a naked couple getting it on. Besides the male and female blocky characters, there was a stamina meter. To beat the level, you had to keep the stamina meter at the top of the screen while the couple engaged in action. In order to keep the meter high, you had to - yep, you guessed it, rock the joystick back and forth (in retrospect, a push-pull joystick would have been a better controller). Gently at first, then with more fury and speed the longer the game went. You knew you were doing fine because the girl would call out "Ja!" (via on-screen text) if you were at the top. If you lost steam, she would get mad and say "Schlaffi!!!" (which Wikipedia tells me is German for "wimp"). Beating the level would give you a different picture and a new girl (actually, the same girl with different colored sprites for hair).