In the movie The Wrath of Khan, Khan says:
Ah, Kirk, my old friend, do you know the Klingon proverb that tells us 'Revenge is a dish that is best served cold?' It is very cold ...in space.
Khan left Earth in 1996. He had only a few days with the Enterprise before being marooned on Seti Alpha 5. Where did he have an opportunity to learn of a Klingon proverb?