The official term for mentally handicapped people used to be "mentally retarded." But it isn't any longer, and besides, I think briandmyers's point was that "retard" was offensive, not "retarded" - he specifically said "any time it is used as a noun" (emphasis mine). Further, the example you gave is flawed because a.) "retarded" is no longer a PC term for the mentally handicapped, so of course people are going to be offended, and b.) clearly, if you're saying "hah hah, you are retarded", the intent is malicious, so taking offense is totally justified. To make a comparison - "The official term for African-Americans used to be the n-word. I think there is a huge consensus that if you went up to an actually African-American person and said 'hah hah, you are a n*' you would be in the wrong."