I did not know of this one- Thanks to Turban Bomb

Back in 1667, the Zaporozhian Cossacks defeated a Turkish army that had been sent in to the south of Russia. In spite of his defeat, the Turkish Sultan, Mehmed IV, sent a letter to the Cossacks, demanding their surrender.

The letter went like this:
As the Sultan; son of Muhammad; brother of the Sun and Moon; grandson and viceroy of God; ruler of the kingdoms of Macedonia, Babylon, Jerusalem, Upper and Lower Egypt; emperor of emperors; sovereign of sovereigns; extraordinary knight, never defeated; steadfast guardian of the tomb of Jesus Christ; trustee chosen by God himself; the hope and comfort of Muslims; confounder and great defender of Christians—I command you, the Zaporozhian Cossacks, to submit to me voluntarily and without any resistance, and to desist from troubling me with your attacks.

A reply was written:

Zaporozhian Cossacks to the Turkish Sultan!
O sultan, turkish devil and damned devil's kith and kin, secretary to Lucifer himself. What the devil kind of knight are you, that can't slay a hedgehog with his naked arse? The devil shits, and your army eats. You will not, you son of a bitch, make subjects of Christian sons; we've no fear of your army, by land and by sea we will battle with thee, fuck your mother.You Babylonian scullion, Macedonian wheelwright, brewer of Jerusalem, goat-fucker of Alexandria, swineherd of Greater and Lesser Egypt, Armenian pig, Podolian thief, catamite of Tartary, hangman of Kamyanets, and fool of all the world and underworld, an idiot before God, grandson of the Serpent, and the crick in our dick. Pig's snout, mare's arse, slaughterhouse cur, unchristened brow, screw your own mother!So the Zaporozhians declare, you lowlife. You won't even be herding Christian pigs. Now we'll conclude, for we don't know the date and don't own a calendar; the moon's in the sky, the year with the Lord, the day's the same over here as it is over there; for this kiss our arse!

Thats what I call diplomacy!
Read it all here.