In the Strip Club you can buy a private dance for 40 dollars. It begins a mini game in which you have to touch and flirt with the dancer until you fill the bar in the right bottom corner. There'll be a bodyguard who will look at you and try to not let that happen. When he is nearby, release RT/R2 used for touching and only flirt with the girl (A/X). When he moves away, press trigger and return to touching. When you get three times spotted by the bodyguard, you're thrown out from the club. You can easily check if he is getting closer. Notice a small breach on the screen between a wall and a curtain. Look at it and stop touching girl when you only notice a move through it. When Trevor takes over club, he can touch girls without paying an attention on security.
When you fill the bar, you may offer her to ride to her or if she can bring her friend for a double dance. Only those girls will agree ride home: Julliet, Infernus and Sapphire. You get their numbers and they'll send you their pictures from time to time. It's necessary for 100 % completion of the game.