Taboos in personal relationships

It is best to call to people in a quiet voice, using their names preceded by Mr. Mrs., or Miss. Waving or beckoning with an upturned finger is considered highly impolite.

If you must silently signal for someone to come toward you, do so by using the whole hand with the palm turned down. Not to do so would indicate an air of authority or superiority over the person being called or beckoned.
 
Never touch anyone on the head as this would be considered as a personal insult to the individual and perhaps even to his ancestors. Many Vietnamese believe the spirit resides there. Hence, the belief is that if a person is beheaded, his spirit will roam forever without finding a resting place. Also, don’t touch anyone on the shoulder.
 
Some people believe that a genie resides there and it is undesirable to disturb him. If you mistakenly touch one shoulder, you must also touch the other shoulder and this helps offset the bad luck.