So what IS it exactly? It's a minigame, where you match up and down controls with CJ's movements. The same download allows for two options: Straight to the action, giving you all girlfriends and automatic 'hot coffee' after each date, OR gameplay friendly which gives you the uncensored action when you earn it like the good cop-murdering boyfriend you are.
The final game in the Grand Theft Auto 3 series didn't settle for just a mere nude patch and instead opted for full on sex. I think the patch for the game may disable this 'mod.'