Good question Polly, I think basically any kind of sexual contact in public that is illegal also applies to nude bathing beaches too although rubbing sunsreen on each other is fairly common although I wouldn't recommend that for you and your bf as from what you've told me he'd be contributing his own sunscreen in your direction

and that would be against the rules!
So I think male orgasms of any kind would be against the rules although you could have one as long as you didn't make it obvious and it was hands-free!