In a country where intellect and action are trammelled and restrained, men of rank and fortune may become idlers and triflers with impunity; but an English coxcomb is inexcusable…
-- Washinton Irving, Bracebridge Hall, or The Humorists, A Medley, 1821
"...He is extremely insinuating; but it's a vulgar nature. I saw through it in a minute. He is altogether too familiar; - I hate familiarity. He is a plausible coxcomb."
-- Henry James, Washington Square, 1880
Coxcomb is a corrupted spelling of cock's comb, the comb of a rooster, hence the badge resembling it that was worn in the cap of a professional fool or jester, hence the wearer of the cap, hence a fool or a vain and silly man.