There's a good chance you'll cross paths with a celebrity now and then...they're people too, if you have to greet them, do so discreetly and they will normally respond.
Stalking is a federal offense here :-)) Gawking can also be counter-productive.
You're In Socal, and as Kurt Cobain once said, "Come as you are!"
There really is no formalities in Socal. Although when walking by, it isn't out of the ordinary to say 'hello' to any passers-by. Just your normal, smile, eye contact, and 'How yah doin'" routine. You'll find you'd get the same response.
Just remember, chances are half of the people you'll see are from somewhere else too, so don't over-do trying to 'belong', be yourself and have a great time.
Well, leave the black socks at home.
It's a tradtion to after a successful cruise to celebrate with champagne or wine, as these people are doing here.