Date: November 25, 1783
Evacuation Day was the day that the British troops sailed out of New York City at the end of the American Revolution. (Not to be confused with Evacuation Day in Massachusetts - where the British sailed out of Boston Harbour, nearer to the beginning of the Revolution.)
While the Treaty of Paris formally ended the war in early September, the British took some time to pack up their belongings and leave their stronghold at New York - mainly because many Loyalists found a sudden need to leave the country, and so there were more people to carry than they originally anticipated. Plus, they probably wanted some time in Duty Free.
Of course, the British are known for being practical jokers, and so they couldn't resist getting in a few friendly parting shots. Before they left, troops nailed a Union Jack to a flagpole on the Bowling Green - and then greased the pole. Undaunted, the Americans nailed up spikes to help them climb, managing to raise Stars-and-Stripes before the British fleet had sailed out of sight. After that, climbing a greased flag pole to tear down a Union Jack would be part of New York's Evacuation Day festivities - proving that you Americans need better hobbies.
The other British parting shot was a literal one - a British ship fired a cannonball at the crowds on Staten Island, who were jeering at the departing flotilla. Nobody was hurt - the ball fell short of the land - but it's sometimes called the last shot of the American Revolution.
Evacuation Day isn't much celebrated any more - it fell out of favour when Thanksgiving was moved to the end of November, in 1863.