Yankee Doodle is so much worse than you think. The Americans re-appropriated it from the British who... marched down the streets and sung it to the local population while they were conducting an questionably legal military occupation of Boston. They suspended freedom of speech, press, assembly, due process, and the right to bear arms. They also seized a warehouse and turned it into a patrol base/barracks in the heart of the city.

Yankee is already an insult. Doodle, is a reference to Americans being basically idiots, so another insult. Dandy... well, it means the equivalent of a "faggot" as a kind of limp-dick, weak-willed, 'fag' (regardless of sexuality). Riding a pony instead of a horse (indicating more weakness and stupidity), decorating himself with feathers and calling it macaroni (which means in his vain attempt to be taken seriously, he dresses like an idiot in order to look like a metrosexual).

They sang that, while marching down the street, at the population of men and women who's rights they had suspended and were explicitly stating they would execute if they got out of line.

... And yet the British wondered why we fucking shot them for it.

Imagine how fucking angry a foreign army would make a population if they marched down the street singing "Kill yourself you stupid faggots"