I discovered this little gem in MAME .66 today while cruising through the games list. Never heard of it before, and I doubt many of you have. It's a licensed take on Activision's Mahjongg tile-matching game, with a sexual twist in addition to the standard 1 and 2 player games.
It's surprisingly well done. The graphics, while explicit, manage to tread that perfect middle ground between outright hardcore and the boring softcore you normally find in an arcade.
The game itself features a nice gameplay twist: the matching tiles must be free to slide at least one direction, and must connect to the partner tile with three or fewer line segments. It's kind of hard to explain, but immediately understood when you see it in action.
After you successfully complete a round you're given a quick intermission bonus round. Each one is different, but each involves rapid button mashing and a girl that gets more and more naked as you pound the panel. If you roxx0r that button you're rewarded with a more explicit single image before you're thrust into the next round of sexy tile matching madness.
It's a lot of fun, and the learning curve is perfectly gradual until you reach about stage 4, when you're presented with a walled off arena (the first without a girl in the background) which is f**king impossible to beat.
It's entirely in German.
The ROM name is rongrong (surprise!). Look it up, snag a copy, give it a whirl.