During my years as translator, I have never heard the word "dude" in any conversation, formal or not. Doing some further reading since your thread really got me interested I confirmed what I previously thought...
dude is an address term that is used mostly by young men to address other young men; however, its use has expanded so that it is now used as a general address term for a group (same or mixed gender), and by and to women.
Dude is developing into a discourse marker that need not identify an addressee, but more generally encodes the speaker’s stance to his or her current addressee(s). The term is used mainly in situations in which a speaker takes a stance of solidarity or camaraderie, but crucially in a nonchalant, not-too-enthusiastic manner.
Dude indexes a stance of effortlessness (or laziness, depending on the perspective of the hearer), largely because of its origins in the “surfer” and “druggie” subcultures in which such stances are valued. The reason young men use this term is precisely that
dude indexes this stance of
cool solidarity.
Such a stance is especially valuable for young men as they navigate cultural Discourses of young masculinity, which simultaneously demand masculine solidarity, strict heterosexuality, and non-conformity.
