Giovanni Boldini/WikimediaAnswer: Well Dressed Men
Ask a modern American-English speaker to pin down where “dude” originated from and they’ll likely guess late 20th-century California surfer culture. Not a bad guess, but a solid century too late.
The word first entered the American-English lexicon in the 1870s and referred to men that dressed very fashionably (with a secondary use to refer to well-dressed urban men who were visiting rural areas and stuck out, what we would now call “city slickers”). In fact, if you’ve ever heard the term “dude ranch” used to refer to a fancier ranch intended for tourists or a hobby ranch owned by a wealthier person, you’re seeing the word in its original use: a dude ranch is a place for well-dressed “city slickers” to go play cowboy.
That usage stuck until the early 1960s when the word was adopted by surfer culture. There, the term dude became synonymous with “guy”—and there was in fact a female version, “dudette”, in use—but by the 1970s, dude become unisex in usage.
Now when someone yells, “That dude is trying to break into your apartment!” they most certainly do not mean, “That very well-dressed gentleman”—although it’s always possible you’re about to be burgled by a man sporting a pocket square and an ascot.