Yeah it sucks when you are trying to go about your own business and someone like him comes along. My first reaction with blowhards like that is to go dead calm.
I then look them in the eye and say, "Better bring a lunch and first aid kit if you wanna try - you'll be here a while."
It's always the first thing that comes to mind. It HAS gotten me into a scrape or two over the years, but nothing big. Ive taken it and dished it out...and survived.
Guys like that are trying to intimidate others and playing on fear. Dont show them any.
DO let the beach patrol know of his plans when you next see them, though. After a few hours, you should have waved at them every time they come by and maybe even gotten to know them a little. They are the ONE bunch of people on the beach you should talk to.