My apologies if anyone at all is actually reading this blog. The whining and raging is not bad coping, it's material for later creative use. And it's working well.
Anyway, the original basis for smiling is that you're happy. And if you're happy, you're less liable to beat the crap out of someone. Thus smiling came to be associated with being a reassuring thing which communicates: "I'm not a threat."
So then even when actually you aren't happy you may still want to communicate that you're not a threat. So you smile even though you're not happy. No big deal. It's not rocket science. Yet, no one could ever explain it to me. Or couldn't be bothered to do so anyway. Oh well.
I think around adults it ought to be understood that we're not threats to each other. Or, anyway, at the very least it ought to be understood that people who actually are threats will smile anyway.
With children perhaps it's different. They're so little and defenseless and dumb. So, sure, smile to show you're not a threat.
But don't treat adults like children. When you fake smile at me, I feel like I'm 8 years old. I know someone who actually is a threat would smile anyway. All you're actually doing is reminding me that we live in a violent world.