Cock feather in a bonnet for civilian attire.

[MacKenzie]

I have it on good authority that it was a fellow named Yankee Doodle. He was apparently riding a pony. I'm not sure what was on his mind, but it may have been a small elbow pasta.

The internet can lead to some strange discoveries.

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. Whether or not these were alternative lyrics sung in the British army, they were enthusiastically taken up by the Yankees themselves.

I've always assumed it was just nonsense.

http://en.wikipedia.org/wiki/Macaroni_(fashion)