Personally, I would not want to greet everyone. I walk by a lot of people in my school, at work, on the street, in the mall, at the movies, anywhere I go. If everyone was well mannered and saying hello... well, that would be bad. I couldn't deal with it. But then again, if there is an incident that two people connect to, they will connect to it. People just need a reason. Go play a pick up game of basketball. The kids there get along. They have something to connect to, a basketball. If a line is long somewhere, people can let out a long sigh and get some sympathy.

Sir and ma'am, I believe, is sort of unnecessary. At least in PA it is. You don't need a sir, or a ma'am to be liked and respected by adults. Just smile, and make sure to wish them a good day.

A greeting I don't like: Hi, how are you? Noone really means the how are you part. They just want you to say hello. It's just an extension that means nothing.