I have my slave tied up to a chair with his ankles cuffed. I stroke his cock and caress his balls until he's about to cum, then I stop and punch him in the nuts instead. I do this a few times, never letting him cum! I proceed to tell him about how I'm going to suck other men's dicks while he watches. I decide to jerk him off until he cums finally, but he takes too long so I make sure to punish him with post orgasm jerking. Hopefully he learns his lesson. :)