If I don't know you and I pass you on the street, chances are, I try to flash you a friendly smile. The thing is, when I do this, I seem to have some problem coordinating my mouth muscles, and so what you get can best be described as an "mmmf" face, the sort of face that Charlie Brown makes when he is eating a peanut butter and jelly sandwich and grunting in assent.
When I see someone I know, I'm freed of my muscular paralysis and able to give that person a genuine, open-lipped smile. Why I can't do this with people I don't know, I'm not quite sure, but I suspect that it has something to do with feeling awkward.
(Sometimes, when I pass large groups of teenages, I forget how to walk and have to concentrate really hard. This doesn't happen nearly as often as it used to, but it does still happen occasionally.)
I'm pretty sure that these are the physical manifestations of intense self-consciousness, and they are difficult to overcome.
So, while my "mmmf" face may possibly still be a friendly face, I'm working on a simple smile, not even a full-force, tooth-showing smile, but just a slight upturn of closed lips. I practiced it in the mirror - I don't have to put forth much effort for it to look real, but because this particular smile feels so unnatural to me, not being my regular, without-thinking smile, I need to work on it. It actually looks fine, but it feels like it looks ridiculous, and I have to keep checking the mirror to make sure it doesn't.
(I've tried the teeth-together smile with lips bared, which some people can pull off quite well, and this actually feels very comfortable on my face, but unfortunately, when I do this, I look like a maniacal beaver readying for the attack.)
Please tell me that I am not the only one who has this sort of problem.