The first high-five was quite a historical event. It was documented by Slapvinius Clapicus, a Roman historian, during the 3rd Century B.C.
“And when the day was won, General Batti-il Cinque turned to his captain and said, ‘Lo, we are victorious! My body cannot contain such momentous excitement, Take thine palm and stroke mine own!’ The captain was confused. ‘Why, General? I have taken an oath not to raise my hand against, nor strike, any of mine superiors. Why doest thou request I break mine oath?’ The General raised his hand in the air, with the palm facing out. ‘Think not on it, captain; simply do as I order, and you shall understand.’ And when the captain and the General struck their hands together, there was a bolt of lightning in the sky, as if that very moment had been orchestrated by Jupiter himself from his throne on the Mount. ‘Huzzah!’ shouted General Batti-il Cinque, making a fist and pumping his arm back and forth, a motion henceforth known by his assistant Guido as ‘the First-Pump.’ The General and the captain shared a grin, and the entirety of the Roman armies cheered, for they knew not what had happened, but they knew it had changed the world even more than their victory over the Huns.”
As you can see, it was documented by a guy with a weird, Latin-sounding name, and written in old English-sounding words (because everyone knows the Romans spoke English in thick British accents.) Clearly, the story above is 100% true. Above and beyond the possibility of all doubt.