October 17, 1961 - The New York Museum of Modern Art hangs Henri Matisse's
Le Bateau upside-down. It remained upside-down for 45 days "until a stockbroker named Genevieve Habert noticed the mistake and notified a guard. Habert later informed the
New York Times, to which Monroe Wheeler, the art director was notified, and the artwork was rehung properly."
Source: Wikipedia