I missed this anniversary by a couple of days, but on the 17th of September 1859, Joshua A. Norton proclaimed himself "Emperor of these United States and Protector of Mexico." Funny thing is, many people went along with it. He made numerous decrees, issued his own currency, (that was accepted in the establishments he frequented) and when he died, nearly 30 thousand people packed the streets of San Francisco for his funeral.
Emperor Norton in popular culture
hat tip: LedgerGermane