How did aviator Douglas "Wrong Way" Corrigan earn his nickname?

Corrigan claimed his unauthorized transatlantic flight was due to a navigational error, caused by heavy cloud cover that obscured landmarks and low-light conditions, causing him to misread his compass. However, he was a skilled aircraft mechanic (he helped construct Charles Lindbergh's Spirit of St. Louis) and had made several modifications to his own plane, preparing it for his transatlantic flight. He had been denied permission to make a nonstop flight from New York to Ireland, and his "navigational error" was seen as deliberate. Nevertheless, he never publicly admitted to having flown to Ireland intentionally.