Mark Peters explains that the word "dude" has evolved over time. In the 1800s, it referred to a dandy -- a person obsessed with proper dress and deportment. The following century, the meaning began to change:
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In the 20th century, “dude” evolved to take on a more neutral meaning. The term was adopted in the black community, then as now a prime spreader of new words and meanings. This 1967 OED example reflected the shift in meaning: “My set of Negro street types contained a revolving and sometimes disappearing (when the ‘heat’, or police pressure, was on) population... These were the local ‘dudes’, their term meaning not the fancy city slickers but simply ‘the boys’, ‘fellas’, the ‘cool people’.” In the sixties, the term attracted more coolness as it was embraced by surf culture, and by the seventies, a dude was just a guy.
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http://i179.photobucket.com/albums/w304/dooflotchie/cat/duder002-1.jpg
A dude is a somewhat estranged wierd surfer/skater/streetbiker-guy that listens to grunge-music, goes to open-air festivals and smokes reefers.
A dudette is a streetwise sassy bit financial upper-class girl.
I'm a 29 year old woman who occasionally calls people dude, male or female. My closest friend also calls me dude. It's not to be cute, or cool, but just comes naturally.
Brought the house down.
I've been trying to use that ever since — never got the slightest reaction.