Poltical Incorrectness or Necessary Speech?

I feel sorry for the young man mentioned in this article, which is somewhat unnecessarily difficult to read as it is a transcription of the television news story.

I like the unanswerable Constitutional law questions in most situations, though, so I think it merits posting. I wonder how a sign using a distasteful but not-truly-vulgar word like "retard" fits into our Constitutional decisions, especially if it is being used by way of protesting inaction by the authorities. I could research it, but sometimes it's more fun just to post the question and open the floor.