DS calls his pals parents by their last names (ie: Mr. and Mrs. Jones). Same w/teachers.
When we introduced DS to our neighbors, we said "this is Mr. and Mrs. Smith" and they said "oh, don't be so formal, call us "Mrs. Luanne and Mr. Marty". So, DS does. In turn, their kids call us "Mr. Mike and Mrs. Susan". Although, they call me Miss Susan (why, I don't know ... but my Kdg. kids and other students in the school often call me Miss W.).
I prefer to introduce my child to someone on a more formal level (Mrs. Doe) ... if the adult wants my child to call them something else, then they can take that opportunity to say that they'd prefer to be called "Mrs. Joan".
In my school, as I have mentioned, many drop the Mrs. and call me either Ms. W. or Miss W (not using initial, but my full last name). I don't know why. I don't correct them b/c at least they're not calling me "Yo, beotch". We do have two teachers who go by Miss First Name. That is their prerogative and do so b/c both have tricky last names. If I had a tricky last name, I think I'd prefer to be called Mrs. Last Initial - like someone named Mrs. Xerchelowchsopolousko (totally made up name) could be called Mrs. X.
Warmly, Daxx's Wife