To masturbate before sex, so as to maintain sexual stamina during sex.
Peter: I don't think Mary will give it up anymore. Every time we have sex I always blow my load right away.
Paul: You really need to start giving yourself a courtesy tug.
Peter: What's that all about?
Paul: It's when you rub one out right before having sex, so as to maintain stamina during sex. You'd really be doing Mary and yourself a favor.