I highly value civility and politeness.
I'm not asking you to jump in cars with strangers, but I do feel that when someone says "hi" to you, whether friend or foe, it is only appropriate to say "hello" back. And smile. Even if it is fake.
I'm sorry if I'm offending you and your future children, but I don't understand kids who just sit and stare at you when you smile and greet them. I'm not saying they are dumb or impolite. Nay, it's by no means their fault. Maybe they are cranky or overstimulated. Or I have a huge zit on my face they can't take their eyes off of. Or they don't have a personality. Or parents that encourage them to conform to society's pleasantries.
You girls certainly aren't at your best every single time to greet or meet someone, but I encourage you to wipe the surly looks off your face, to smile, to recite the Periodic Table of the Elements, or something to that effect.
We've also been working on our courtesy laugh. For those times when people (or your dad) think they are wittier and more charming than they really are.
You're welcome. For being your mom. For teaching you useful things. And being generally awesome.