was originally a slang term in 1880's New York. From the OED:
A name given in ridicule to a man affecting an exaggerated fastidiousness in dress, speech, and deportment, and very particular about what is æsthetically ‘good form’; hence, extended to an exquisite, a dandy, ‘a swell’.
One possibility is that dude
came from dud
, meaning "an article of clothing." The dude
of "dude ranch" probably comes from well-dressed Easterners taking a vacation on ranches. During the 1930s, dude
came to mean a generic "guy," leading eventually to surfer lingo. The Word Detective has an article on dude
It's funny how a dude
was originally a fancy dresser to today's sense of dude
as more of the slacker type.