Though the term seems distinctly American, it had an interesting birth: one of its first written appearances came in 1883, in the American magazine, which referred to “the social ‘dude’ who affects English dress and the English drawl”.
The teenage American republic was already a growing power, with the economy booming and the conquest of the West well under way. But Americans in cities often aped the dress and ways of Europe, especially Britain. Hence dude as a dismissive term: a dandy, someone so insecure in his Americanness that he felt the need to act British. It’s not clear where the word’s origins lay. Perhaps its mouth-feel was enough to make it sound dismissive.
By the 1950s or 1960s, dude had been bleached of specific meaning. In black culture, it meant almost any male; one sociologist wrote in 1967 of a group of urban blacks he was studying that “these were the local ‘dudes’, their term meaning not the fancy city slickers but simply ‘the boys’, ‘fellas’, the ‘cool people’.”
From the black world it moved to hip whites, and so on to its enduring associations today—California, youth, cool. In “Easy Rider” (1969) Peter Fonda explains it to the square Jack Nicholson: “Dude means nice guy. Dude means a regular sort of person.” And from this new, broader, gentler meaning, dude went vocative.