I’m stickler for formality - I call EVERYONE (except personal friends and family members) Mr., Mrs./Ms./Miss, Dr., Rev., Gov., M’Lord, Gen., Prof., Czar, or whatever other honorific seems appropriate - until they tell me explicitly what to call them. That includes friends’ parents, co-workers, flight attendants, telemarketers, bouncers, sideshow freaks, you name it.
I’ve never met anyone who was actually offended by being titled (though some people are a little amused), but there are those who get annoyed if you call them by first name without being invited to do so. In my ongoing effort to avoid confrontation at all costs, I tend to be overly polite.
That said, if I were a friend’s parent, I wouldn’t mind being called by first name. Actually, anyone is welcome to call me by my first name. Provided they can figure out how to pronounce the asterisk. 
