I just expect people to not degrade me by demanding that I alter my appearance for them.
When people tell you that you should smile more, they are not demanding that you alter your appearance for them. They are saying that they find your smiling face pleasant and request that you display it.
I smile when I feel like it, and if I don’t feel like smiling then I don’t smile.
It is easier to tolerate the general stresses of life when one is not hanging around people who grump. Having friends who are happy when you are around them helps ones mood.
I’m not grumpy in person, at least not all the time. I find it insulting and quite disgusting to expect someone to display a smile even if they aren’t happy or cheerful enough at the moment to do so on their own.