I hate to pick on a random comment but anyway
"smiling actually makes you feel better and also others who are smiled at."
I strongly recommend girls over age about 11 NOT to go around smiling at everyone as it's highly likely to result in a bad scene for them, and an inability to go about their business without interruption.
I suppose if you don't smile you get shit for that as well
But for sure going down the high street smiling at all and sundry is going to result in some pretty tricky attention
I learned to keep my head down fairly young - this may be area specific.