Yankee Doodle's headgear explained.

'Stuck a feather in his cap and called it macaroni.'

A macaroni (or formerly maccaroni)[1] in mid-18th century England, was a fashionable fellow who dressed and even spoke in an outlandishly affected and epicene manner. The term pejoratively referred to a man who "exceeded the ordinary bounds of fashion"[2] in terms of clothes, fastidious eating and gambling. Like a practitioner of macaronic verse, which mixed English and Latin to comic effect, he mixed Continental affectations with his English nature, laying himself open to satire:

There is indeed a kind of animal, neither male nor female, a thing of the neuter gender, lately [1770] started up among us. It is called a macaroni. It talks without meaning, it smiles without pleasantry, it eats without appetite, it rides without exercise, it wenches without passion.[3]
https://en.wikipedia.org/wiki/Macaroni_%28fashion%29



"Young men who had been to Italy on the Grand Tour had developed a taste for macaroni, a type of Italian food little known in England then, and so they were said to belong to the Macaroni Club.[5] They would refer to anything that was fashionable, or à la mode, as 'very maccaroni.' [6] Horace Walpole wrote to a friend in 1764 of "the Macaroni Club, which is composed of all the traveled young men who wear long curls and spying-glasses." The "club" was not a formal one: the expression was particularly used to characterize fops who dressed in high fashion with tall, powdered wigs with a chapeau bras on top that could only be removed on the point of a sword."

"The song "Yankee Doodle," from the time of the American Revolutionary War, mentions a man who "stuck a feather in his hat and called it macaroni." The joke Dr. Richard Shuckburgh, British surgeon and author of the song's lyrics, was making was that the Yanks were naive enough to believe that a feather in the hat was a sufficient mark of a macaroni."

So now you know.