"You are staring at that woman in such a fixed/repetitive way as to be embarrassing. You are embarrassing me, you are embarrassing yourself, and you are probably making her feel very uncomfortable if not threatened.
If you do it again I will WALK OUT."
He does it again.
You walk out.
"You're staring", "No I'm not" is toddler-level behaviour. Is he on the ASD spectrum? If not, he should know that everyone around him knows he is staring, and if he doesn't know, then he bloody well needs to. He seems to think he's getting it past you. (No offence meant to ASD etc.)
I hate this crap. (Can you tell?!) I don't do it, and my DP doesn't do it. I don't agee with all this "oh it's natural","everyone notices attractive people" - like so many things, some people do it blatantly, some do it privately, and some don't do it at all.
Sure, your mind is your own, but you don't embarrass other people about it unless you are seriously socially challenged. If he can manage to refrain from whacking off in the restaurant, he can manage to refrain from this.