I think we all do this every once in a while. I guess we better stop…
From The New York Times:
The Claim: A Fake Smile Can be Bad for Your Health
By ANAHAD O’CONNOR
Published: February 21, 2011
A study looked at bus drivers because their jobs require frequent — and generally courteous — interactions with many people.
Are you a “fake smiler”?
DENNARR(dot)COM 
I smile with my eyes 🙂