A Diagnostic Label Is Not an Insult
"That was such a retarded thing to do."
"He's so clueless, what is he, autistic or something?"
"You're acting like a total spaz."
Now, I'm fairly sure that most of the people who talk like this are being thoughtless, rather than intentionally hateful. If they had ever considered the possibility that they might be overheard by someone who actually had a diagnosis of Mental Retardation, or Autism, or Spastic Cerebral Palsy, they'd have chosen their words more carefully. But such language is so widespread in our society that millions of people just repeat it without thinking about it.
And then there's what I would call the flip side of using a label as an insult: Taking great offense to any criticism of one's behavior, out of fear that others might suspect that one has Big Bad Behavioral Disorder Cooties. Here are a few examples of that:
"How dare you slander me by saying that I have problems controlling my temper! I'm perfectly sane and nothing at all like Those People who go to anger management counseling!"
"Someone told me I was being passive aggressive in a conversation. I'm extremely insulted by that because there is an official psychiatric category of passive aggressive personality disorder."
"What do you mean, I'm too defensive? Are you suggesting I'm some kind of psycho?"
Once again, I think that in most such cases, it's a matter of thoughtlessness and not outright hate. The person who took such umbrage to the words "passive aggressive" probably never stopped to consider the social implications of insisting so vehemently that she wasn't at all like those with an official diagnosis. I'm sure it never even occurred to her that by equating a diagnostic category—which no one had suggested that she actually belonged in—to an insult, she was adding to the stigma against those who really were diagnosed in that category. That's often the way stigma works; it's like a children's game of Hot Potato, where everyone is so anxious to get it away from themselves that they don't care who ends up with it.
Sometimes, people just need to stop and think before they speak.