During interaction between two people, it should not be disturbed, unless it is very necessary. Such behavior can lead to negative thoughts in people's mind. So do not prohibit your child to behave like this.
Why not comment on someone's character or physical characteristics, if it is not appreciated.
It is important to always teach your child to get permission. Then whenever he can not understand anything or ask you for the good before doing anything.
To express gratitude, to teach you how to write a note of gratitude. Especially when he receives a gift from someone, it should not be opened or used before giving thanks to the provider.