Good for the restaurant manager for not standing up for it for himself or his staff. It's bad enough when an ordinary person acts up for some attention and free drinks/meals, but JC is neither short of attention nor money, so it must be purely a bullying/power game for him. Also, unlike some unknown nobody, he must know that the news will get out - so he doesn't even turn on the pretend charm.
Shame, as I really do love Gavin & Stacey.