" Smiling Bloopers

• Insincere smiling can backfire! (Different from a shy smile that just beckons a friendly "hello.")
• Transitioning from a smile to a straight face, too quickly, may give others the impression that you are fake or do not like them.
• Going overboard and smiling all the time, especially when it is inappropriate, will make you appear insincere.
• If your mouth smiles, but your eyes don’t, there is a disconnect that can make you appear less authentic and trustworthy. "

― Susan C. Young , The Art of Body Language: 8 Ways to Optimize Non-Verbal Communication for Positive Impact (The Art of First Impressions for Positive Impact, #3)