Sex doesn't exactly abound in this play. It does come up in a few different sections though. First, when the Player keeps alluding to how Ros and Guil can get caught up in the action, he's basically saying that he'll put on a smutty performance just for the two of them. Guil is offended by the Player's willingness to put on this voyeuristic show for him and Ros. As a result, he slaps him and calls him a pornographer.
Second, as Guil and Ros recall what happened to Hamlet, they note how Hamlet's uncle Claudius "slipped in" with his mother after he killed Hamlet's father (1.547). Ros, referring to Hamlet's father, says "His body was still warm" (1.548). Guil quickly adds, "So was hers," this time referring to Hamlet's mother (1.549). The little joke has to do with the fact that Gertrude marries (and presumably begins sleeping with) Claudius very soon after her husband's death. Not only did Claudius kill Hamlet's father and usurp the throne – he's sleeping with Hamlet's mom (off-stage, however).