Folklore has it that during the famous 1492 landing in the New World, Christopher Columbus had an incredible meeting with Chief Tecumseh. The great indian chief raised his hand in the traditional manner and greeted Mr. Columbus with the customary address, "How". Confused at this manner of greeting, Columbus proceeded to raise his hand and "slap" the hand of Chief Tecumseh. This historic event changed communication forever. Today the High Five is the preferred greeting of sports fans everywhere, all thanks to Columbus and Chief Tecumseh. Believe it, or not.
(Disclaimer: no actual historical events were harmed in the making of this Overlooked Holiday.)