If you work at Quickieburger or the River Rat customers may occasionally ask for sexual favors, and you can ask for money in return.
At Quickieburger customers sometimes ask "so how much for a quickie?" and if your disinhibition is high enough you can give an amount, and they may take you up on it. At the River Rat they may ask for your underwear, or oral, or a thigh job, or full sex, etc.
edit: It's been in the game so long I forgot about it but idk if you know: You can also bet money at the arcade. If you lose the winner may do sexual things to you. And every weekend there's a video game tournament and if you lose then you either have sex with the person who takes #1 or orally service everyone who does better than you. You get paid for doing either one.