There was a famous hot coffee incident where a hacker made that happen, like a mini-game of sex, however you can have sex with your girlfriends or prostitutes, you can hear moaning, but can't see it. Prostitution happens when one comes to you and says, "Wanna have a good time?" Say yes, {right d-pad,} and that's it, kill them for your money back.
Well there are prostitutes. There is "sex" but it is just the car shaking or moaning when your GF invites you in(I think they have moaning I can't remember). The infamous Hot Coffee mod was shut down long ago, and you needed Action Replay for it anyway.