If we pretend to smile, the reaction against other person deep inside our mind will make us produce a stern smile and a smile that is controlled which we called "force smile" which can immediately be identifirnd as an unsincereone.
The method to overcome this feeling is by goung through the dource of our problem changing the negativr image of our ourselves chabging the bad impression of ourselves and finally by telling ourselves that we are not that vicious and that ee still have some virtues then smile at yourself.