Tons. Wars have started over it.

The most severe example is the trash talking between Timur the Lame, Sword of Islam, and Bayezid the Thunderbolt, Master of the Universe. Bayezid and Timur disliked eachother and encroached on each others borders, so they wrote increasingly angry letters against each other until Bayezid insulted one of Timur’s wives. Timur invades Bayezid and took him prisoner for the rest of his life. By one (possibly apocryphal) account, he used Bayezid as a footstool- a literal Ottoman.

The Ottomans were apparently prone to this. After they recovered, Selim the Grim had another feud with the man who had killed Timur’s descendants and made drinking cups of their skulls - Ismail the Sinner of Persia. The two sent angry poetry to each other (the equivalent of a “rap battle”) until Ismail enraged Selim by sending him a box of opium. This implied that he must have been writing his angry poetry while high. By another account, Ismail sent Selim a box of poop, and Selim sent him fruit with the letter “since we seem to be sending eachother what we eat” attached. The two went to war.

Ismail later sent a letter to Selim’s som, Suleiman the Magnificent, praising him for winning a battle against the Christians. Suleiman retorted by calling him “dervish holder” (Ismail was only a small ruler before conquering Iran and Iraq).

This seemed to take place mostly between countries that did not share a common culture and diplomatic tradition. When they did, communication was more cordial. For example, the aforementioned rude Timur the Lame sent comically friendly letters to his main rival, Tokhtamysh of the Golden Horde, another Turko-Mongol Khan. When Timur invaded Tokhtamysh, Tokhtamysh ask his friend kindly remove his forces, and Timur insisted he was just visiting and eager to greet his old friend.

In another example, Nader of Persia when invading the Mughal Empire, which shared Persia’s court culture, forced the Mughal Emperor to greet him as a “friend” and present tribute as a “gift” which Nader graciously accepted.

Most European formal correspondence was cordial. A notable exception was a letter sent by Peter the Great of Russia to Charles XII of Sweden telling him that “you are not Alexander [...] and I am not Darius”, in reference to Charles’ fantasy of conquering Russia with a small but disciplined force.

Leaders of course continued to trash talk one another behind each others backs. Otto von Bismarck said Napoleon III’s “sentimentality exceeded his intellect” and that “schemes multiply in his head like Rabbits” to other European heads of state.

In the modern age with the arrival of mass media, direct insults became common as they were aimed at the audience, but the nature of mass broadcasts necessitated that their targets would receive them too and be able to reply. One of the earliest occasions of “televised replies” was when Hitler read a personal letter from Roosevelt aloud on live television. He mocked Roosevelt for insisting he not invade a number of “sovereign” countries that were not independent to begin with, including Iraq and Palestine, allies like Finland and Italy, and insignificant countries like Luxembourg and Liechtenstein.

Televised replies would later become a political staple, preceding the political social media arguments of today.

Sources:

Marozzi, Justin: Tamerlane, Sword of Islam.

Amanat, Abbas. Iran: A Modern History.

Kling, Stephen. The Great Northern War Compendium.

Overy, Richard. The Road to War.