U. Pittsburgh Linguist Scott Kiesling has researched how young Americans use the word “dude:”
… the four-letter word has many uses: in greetings (“What’s up, dude?”); as an exclamation (“Whoa, Dude!”); commiseration (“Dude, I’m so sorry.”); to one-up someone (“That’s so lame, dude.”); as well as agreement, surprise and disgust (“Dude.”).
Wil Wheaton covers some of the multiple uses of ‘Dude’ in his book, “Just a Geek.” I was lucky to attend two of his readings when he covers the use of ‘dude’ between himself and his brother.
-Chris