A more sensible rule: If I'm wearing headphones in/over both ears, it's possible I can't hear you, so you might want to make sure you have my attention before

A more sensible rule: If I'm wearing headphones in/over both ears, it's possible I can't hear you, so you might want to make sure you have my attention before you talk to me from behind for ten minutes then get upset when I don't respond. Actually, forget the headphone part of that rule.