When you have to kill a man, it costs nothing to be polite. Winston Churchill
Be polite to all, but intimate with few. Thomas Jefferson
It is not enough to be wrong, one must also be polite. Niels Bohr
I do not see why I should be polite to tyrants, who slobber of humanitarianism and think only of their own petty interests. Paul Karl Feyerabend
Anyone can be polite to a king, but it takes a gentleman to be polite to a beggar. African Proverb
If you have no money, be polite. Danish Proverb