1883, "fastidious man," New York City slang of unknown origin; recent research suggests it is a shortening of Yankee Doodle, based on the song's notion of "foppish, over-fastidious male" (compare macaroni). The vogue word of 1883, originally used in reference to the devotees of the "aesthetic" craze, later applied to city slickers, especially Easterners vacationing in the West (as in dude ranch "ranch which entertains guests and tourists for pay," attested by 1921). "The term has no antecedent record, and is prob. merely one of the spontaneous products of popular slang" [Century Dictionary].
Now, "tenderfoot" is not to be construed as the Western equivalent of that much evolved and more abused specimen of mankind, familiarly styled "dude." For even the Montana cowboy recognizes the latter. Not that he has ever seen the true prototype of a class that was erstwhile so numerous among us. But he is convinced that a person caught in the act of wearing a white linen collar, and who looks as though he might have recently shaved or washed his face, must be a dude, true and proper. ["Random Notes and Observations of a Trip through the Great Northwest," The Medical Record, Oct. 20, 1883]
Application to any male is recorded by 1966, U.S., originally in African-American vernacular.
1883, "the dress, manners, and social peculiarities of the class known as dudes" [Century Dictionary], from dude + -ism.
The dude possesses in his outward appearance and bearing all the attributes of a gentleman, excepting, perhaps, that of manliness. His dress is unostentatious in its perfection, its only loud notes being a pair of white gaiters, which are believed to be going out already in obedience to the unwritten code of dudeism. Why the dude feels any interest in life is not clear—he does not look as if he enjoyed it. There is a certain introspective earnestness in his bearing that reminds one of the theological student, and perhaps the prevailing high collar strengthens the resemblance. [Phrenological Journal, July 1883]
derogatory for "Italian," 1912, American English slang, apparently from southern Italian dialect guappo "dandy, dude, stud," a greeting among male Neapolitans, said to be from Spanish guapo "bold, dandy," which is from Latin vappa "sour wine," also "worthless fellow;" related to vapidus (see vapid). It is probably not an acronym, and the usual story that it is one seems to date only to c. 1985.