pinskal, “Dude” is both approbative and gently mocking; a word used among friends. If somebody fucks up in a comical fashion, they are totally “dude.” One is unlikely to call a serious enemy “dude.”
There is an element of lightness and unseriousness associated with “dude,” which is to its credit. See also “dude ranch,” or Chester A. Arthur, the “Dude President.”