Why macaroni?

"Yankee Doodle went to London
riding on a pony
Stuck a feather in his cap
and called it macaroni..."

But why macaroni?
It actually has nothing to do with pasta. The lyrics to Yankee Doodle are a hodgepodge of different choruses with varied origins. The first line, though, is probably a mockery by the British of the uncivilized Americans (...a mockery that the unpretentious Americans gladly took up themselves and incorporated into their own songs.)

It comes from the Italian word maccherone -- a boorish fool. Rich young men who had returned from Italy (it was fashionable at that time for young people to make a trip to Italy... much like many young Americans now undertake a EuroTrip as college students) began using the word to describe something fashionable; we might read the song as, "...Stuck a feather in his cap / and called it trendy."

The lyrics mean that the typical Yankee (the typical American) was so naïve that he thought he could be fashionable simply by putting a feather in his cap.

The word macaroni could also be used as a noun. A Macaroni (or a Dandy) was the 18th-Century equivalent of the 17th-Century Fop, a man who is overly fashion-conscious, urbane and almost effeminate. He was the forerunner of the modern Metrosexual.

The Macaroni Penguin, incidentally, also draws its name from this type of person, because penguins appear to be formally-dressed.