When you offer advice on etiquette, it is asked for, and very helpful. I'm wondering about adults who feel compelled to offer other adults advice on etiquette when it is not asked for. Would offering unsolicited etiquette
advice be considered improper etiquette?
Offering unsolicited etiquette advice would be okay depending on the intent and when it was offered. If the advice were given with good intent such as helping someone avoid doing something very embarrassing, then it would be okay. If the intent was to point out someone's faux pas after the fact, then it was more than improper, it is completely rude.
There are occasions when unsolicited etiquette advice should be welcomed such as business situations and when visiting foreign countries where manners and conduct are more scrutinized and on which one's professional success may depend.