With manners and etiquette on the decline, Do you ever feel it is almost a burden to know what others don't?

Indeed. All you can do is refuse to sucb to the pressure to let your own standards slip. For example, it drives me crazy when people use my first name uninvited. It's rude to correct them, so I set an example by calling them Mr/Ms whatever until they get the hint. If they don't get the hint, I complain to management. If they try to force this presumptuous intimacy on me further by only telling me their first name, I call the Mr John or Ms Denise until they get it.