I know some people get annoyed with me when I asked them to not use the word "retard" or "retarded." In the early years when Eliza barely spoke and would bang her head on the floor seemingly endlessly or exhibited some other non-typical behavior, I heard the word from adults and children alike (I assume the children learned it from their loving parents). When I heard the word I wanted to quite literally, beat the person senseless, but that's not really productive. now is it?
Robert Rummel-Hudson has blogged on why we should refrain from using this word as a derogatory term and the effect that using this word has on parents of special needs children and the children themselves. You can read his views on his blog.
Now do you get it?