I remember telling my grandmother that some people are stupid. Stupid cause they cannot understand you. Cause they cannot tell if you're smiling or showing your teeth. And my grandmother told me that nobody is that stupid. She told me the truth; that people just don't care. Simple as that. They don't care to understand you. And that it would be such a waste of energy trying to understand everybody. People just interpret your reactions according to their "code" or according to the way it suits them.
So I guess we have to accept that and move on instead of dying trying to make clear that this is not a smile...