“Stuck a feather in his cap” is the correct continuation of the “Yankee Doodle” lyric. The line humorously describes a supposedly unsophisticated Yankee trying to look fashionable with a makeshift plume.
“Yankee Doodle” originated among British forces during the French and Indian War, before becoming closely associated with the American Revolution. The song’s early verses mocked colonial troops, but American soldiers and civilians gradually reclaimed it as a patriotic song. It is now the official state song of Connecticut.
The next line, “and called it macaroni,” is often misunderstood as a reference to food. In 18th-century British slang, “macaroni” meant an excessively fashionable or affected person. A feather in a cap was therefore a comic imitation of elite style, not merely an ordinary hat decoration. “Cap” is the traditional wording; “hat” may sound natural in modern English, but it is not the canonical lyric.