Girl, why aren't you smiling? Smile! I'm here so everything's cool.
Why are you saying such things to women that you don't even know?
It's a beautiful day out there so stop being grumpy and smile!
Women are right to be apprehensive about smiling at strangers in public, because they have to be on guard against people taking advantage of them.  If they try to be friendly, a lot of men think that they are being seductive and try to take advantage of them.  Try to be friendly to women, instead of demanding that they be friendly to you, and their demeanor will certainly improve.