The Chazon Ish would stand up for people like this -he said they have holy Neshamos.
So the only reason for s/o to make fun of them is because they are jealous. If s/o is jealous -is because they know how low their own Neshoma is!
I don’t think the word “Retarted” in itself is derogatory, it depends how it is used. I don’t agree with those (PC gurus) who say not to use it. We lost a word from the English language to the Toeivaniks, we shouldn’t lose more words; just don’t use it in a negative fashion.