“To say nothing, especially when speaking, is half the art of diplomacy.”
“Diplomacy is the art of saying "Nice doggie" while looking for a bigger stick.”
“That wasn't English she was speaking: it was the language of diplomacy.”
“diplomacy, n.: The patriotic art of lying for one's country.”
“Diplomacy is the art of letting someone else have your way.”
“Diplomacy is the art of letting other people have your way.”