How to ask?

I once offered my cock when I spotted an elderly couple blowjob on the beach. It had made me very horny and I was so very hard. The woman sat on her husband's cock and gently jerked mine while I kneaded her tits. Then I squirt my sperm properly. In return, the wife obtained that I jerk her husband's cock to cum, which I was very happy to do. It is a matter of honour. Still, I often meet people who masturbate on the beach or have sex with each other. But, I don't dare to ask if I can bring my penis into the game. What do you think? How do you do that? Do you ask everyone or do you just masturbate?

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