Dude, What's Up With the Word "Dude"?
Scott Kiesling believes that use of the word among men is a symbol of what he calls "cool solidarity":
Cool solidarity is especially important to young men who are under social pressure to be close with other young men, but not enough to be suspected as gay.
"It's like man or buddy, there is often this male-male addressed term that says, 'I'm your friend but not much more than your friend,'" said Kiesling, whose research focuses on language and masculinity...
He found the word taps into nonconformity and a new American image of leisurely success.
Kiesling studied tapes of college students going back to 1993 to develop his "dudist" theories. Among the "rules" for applying the word he found were its use between genders (girls sometimes use it amongst themselves; guys can call girls "dude" if they are good friends but not romantic) and within social hiearachies (authority figures such as parents, bosses and teachers are not "dudes").
Kiesling says that "dude" has been around since the 1800s, but caught on in its present form after the release of the popular 1981 movie Fast Times at Ridgemont High, which influenced a generation of "slackers." And although that generation has grown up and are now parents themselves, they never fully left behind those roots.