I'm hoping to hear from some with everyday Italian knowledge about the proper use of formality. I know what the books/guides say that the informal is family and close friends but how egregious an error is it to incorrectly address someone informally?
One example - I was in a not very touristy town and getting a snack and the woman who ran the bar brought me half a panini and was profusely apologizing because she dropped half of it on the floor transferring it to the plate from the press and while she was making me another one I would have to wait for the second half. She seemed really upset and while we I had ordered in English - or some mix of English and bad Italian - I had studied enough to know "Non si preoccupi" - Don't worry about it (formal). This really seemed to make her feel better.
Now I was glad that the proper phrase popped into my head at that moment but how bad would it have been to say "Non preoccuparti" - Don't worry about it (informal)? In my mind it seems like addressing someone who runs a shop and is apologizing informally might make you seem very condescending, but that's the cultural part I have a question about.
Obviously I'd probably get some slack as someone who is clearly a non-native and beginning learner but without that benefit of the doubt would that have come off as insulting? Or rude or not that big a deal?
Thanks,
=Tod