"Did you see him do that? I knew dude was crazy, but I didn't expect *that*".
This reads/sounds alright to me, but if it was "man" or "guy" instead of "dude" in the second sentence up there, I'd expect "the man" or "the guy".
Another context where this happens is at the beginning of a sentence. Something like: "I'm so glad she finally dumped him. Dude is the scum of the earth." Again, a different word would seem strange without the article.
Some google counts and search results seem to support this feeling (e.g. search for "I knew dude was", compared to "I knew man was" or "I knew guy was").
English isn't my native language, so I could be making it all up! Which is why I'd love to have some feedback to go with this gut feeling. Like, do you agree that there's something peculiar going on here? Are there other words which behave like this besides "dude"? Is this perhaps a regional thing? Is it recent? Do linguists have a word for it? (more specific than just 'zero article', I mean).