First said by Pierre Ambroise Francois Choderios de LaClos (1741-1803). He originally said it in French in his 1782 book Les Liasons Dangereuses: "La vengeance est un plat qui se mange froid. Quoted in Kill Bill Vol. 1 as being an old Klingon Proverb
"Why did you brutally murder all of the people who killed your unborn baby?"
"Revenge is a dish best served cold"