Pornography is featured throughout the GTA series.
Appearances in GTA series
In Grand Theft Auto: Vice City, there is a pornographic film company (InterGlobal Studios) on Prawn Island, run by Steve Scott. Several missions involve working for Steve, including meeting prostitute/porn star Candy Suxxx.
There are a number of sex shops in GTA IV and Grand Theft Auto: San Andreas, some of which can be entered. There are shops which can be entered in Hove Beach, Star Junction and on the Las Venturas strip.
In every Pornographic Shop of GTA IV, there is a small TV playing, it is only just a repetition of a girl going up and down, implying her vagina being humped.