 During the scene at the Chinese theater, Bill the Butcher calls for  his boys to play some "American music" and extols it as "patriotic."  The tune they play is "Garry Owen," a Gaelic drinking tune, which  became the official song of the 7th U.S. Cavalry Regiment, chock  full of Irishmen and infamous for their defeat, along with their  commander, Gen. George Armstrong Custer, by Indians at Little Big  Horn.