I'm currently living in an area where manners mean a lot. By and large, people are friendly and polite as a matter of course. They smile at me on the street. They make small talk with strangers. After living here for over a year, I've started addressing older strangers as "sir" and "ma'am". It's a little old-fashioned, but it goes over well.
Unless I'm at a play party, in which case it is very bad form to assign those titles to someone with whom you don't actually have an existing power dynamic. Anyway, I don't want to be giving anyone ideas.
So I do a lot of "Excuse me, si... uh, 'scuse me."
I am going to be putting my foot in my mouth one of these days.