It may take more facial muscles to frown than it does to smile. So... keep smiling :)
That is what I usually hear from my clients (and friends). Smile per se, can according to some behaviorists improve mood temporarily, via facial muscle movements that trigger further reactions, but the other branches of psychotherapy see that more as some kind of hysterical phenomenon.
It is not easy to smile constantly while working, people who's jobs require smiling, like costumer service, are subjects of
emotional labor that can cause a burn out or severe emotional exhaustion.
I understand rudeness, if emotional prostitution is not rewarded accordingly.
So, Poles and everybody else, be rude, if you are payed less ;)
Genuine feelings expressions are the sign of emotional maturity, and that is the healthiest reaction possible. Mechanisms used to overcome anger, sadness, fear are payed later. Expensive tricks.