I decided not to look for references since I did not want to point anyone out, however I think we have all seen a rude comment on a poorly posed question several times.
There appears to be a sizable camp who believes that not putting effort into a question is "rude" and that it's then OK to be rude back. This can take different forms, a commenter might for example tell the OP off, or attack his person, or make fun at his expense.
Personally I feel that if you do not like a question, do not spend another minute to tell the OP unconstructively how he's "wasting your time." Move on instead, possibly with a vote to close if that is applicable.
The thing is, there are many users on this site who are very good at giving constructive criticism and I've seen it in even pretty hopeless cases. So personally when I see someone being rude I ask myself whether that person could not simply have waited for one of those other users to say something, or wait for the question to be closed, because when it is there is also a constructive explanation as to why it was closed.
What do people think? Are there cases where it is justified to be unconstructively rude? It could be good to have a source when a discussion like this comes up that you could point at and say, "the community at large thinks that..."'
Edit to clarify: I don't think this community is rude at all. The incidents that I think of are very rare. But when they happen it seems to be because of a difference of opinion of what is acceptable/justified/fun with no harm done, so there does seem to be a difference in opinion.
Regarding the comment that says that this can't be discussed, it is probably true.