Teachers were always addressed by Mr/Mrs/Ms and this extended into Scouts as well. For anyone I don't know, I tend to just say "sir/ma'am" (employee at the grocery store for example) unless. If the person has a professional title that I know of, I will use the title (Dr. Martin, Professor Lake, etc).

My parents I suppose were very similar. Sir/Ma'am for most interactions, but I don't recall hearing a Mr/Mrs/Ms when they referenced other people in our lives.

Since I've moved to Europe a few years back, I'm trying to follow the local customs more, which at first glance seem very similar (Netherlands). Formal for strangers, informal for basically everyone else. I've tried using the formal with some older neighbours and they always tell me stop immediately!

That brings up an actually interesting exception. At my church, the pastors were the only adults we'd ever call by their first name, sort of. Our pastor, for example, was always Brother Mike, not Pastor <Last Name>.

I think this is also true for Orthodox monks.

I'm not sure if there's a Christian denomination that has pastors who aren't priests, and also has monks. So this sounds to me more like a situation where all fellow members of the church are addressed as Brother/Sister.

I also grew up in Texas and to this day I still tend to use sir/ma'am for most adults I don't know. Every now and then it seems to throw people off. People don't seem to expect to hear "Yes, sir" very often it seems.

Conversely, in coastal California that kind of speech is actively (even aggressively) discouraged, such as in public schools, higher grades, especially. It's still appreciated in more traditional communities, though, such as black or immigrant Asian communities. Code switching isn't limited to certain minority groups; even affluent coastal white folks often end of code switching.