The vast majority of people who ride bicycles are not aware that there is any such thing as cycling etiquette, so you first have to get their minds over that hurdle. I encounter this at work, where the two other daily bike commuters think I'm a crackpot because I don't generally ride on the sidewalk or the wrong side of the street, I signal turns and stop at stop signs, sometimes take the lane, make vehicular left turns, etc. I have on occasion mentioned various aspects of good cycling technique and they basically reacted as if I'd said something insane. People who use their bikes to get around are often not interested in cycling as a thing in itself, and consequently have almost no exposure to cycling culture and the ideas those within it take for granted. When you say they should learn, you're forgetting that there really is no readily available source of knowledge for them.