E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A coxcomb (Italian, un maceheróne). The word is derived from the Macaroni Club, instituted by a set of flashy men who had travelled in Italy, and introduced Italian maccheroni at Almacks subscription table. The Macaronies were the most exquisite fops that ever disgraced the name of man; vicious, insolent, fond of gambling, drinking, and duelling, they were (about 1773) the curse of Vauxhall Gardens.
We are indebted to the Macaronies for only two things: the one is the introduction of that excellent dish macaroni, and the other is the invention of that useful slang word bore (boar), which originally meant any opponent of dandyism.Cassells Magazine: London Legends.
An American regiment raised in Maryland during the War of Independence, was called The Macaronies from its showy uniform.