In Russia you have to look angrily at strangers :-). A while ago I read a story how the first MacDonald in Moscow taught their people to smile like americans do and how disturbing this was to the Russians first.
Maybe I'll stop smiling briefly when I pass by someone who will just misunderstand it; but when I'm with myself and the world, or with people or animals who are content, I smile a lot. Why not? Not doing so would be the mental equivalent of not just smoking, but lighting cigarettes with hundred dollar bills.
Only if you want them to think that you're normal :}