Wow -- this study, published in the NY Times, focused on bus drivers. Anybody who has waited on tables can see the connection!
It turns out that pretending to smile and be happy when in a bad mood worsens the bad mood. So, smiling and being gracious to one rude table can ruin the entire evening -- any waitresses out there disagree? Another interesting finding was that this phenomena hurts women more than men. I consider waiting tables a female job even though some men do it -- similar to teaching and nursing. The article states that women are more geared to express emotion and therefore hiding and faking emotion has a stronger negative effect on us.
Another aspect of the study is that thinking positive thoughts in an attempt to smile and be gracious helps keep one's mood positive. Focusing on something happy is a true help. Perhaps picturing rude diners in the morgue will make that smile more sincere and lift a waitress's mood.
Can a Fake Smile Be Bad for Your Health? - NYTimes.com