It’s a word I would use sparingly, and on in reference to someone who is being intentionally stupid. And only in the company of people I know aren’t offended by the word. I have a coworker who has expressed how much she hates the word because she has a developmentally delayed sister. So I would never use the word in her presence.
FWIW, I was called “retarded” all the time growing up because I was a clumsy kid who talked funny. It hurt so much to be called that, and I think it caused me to carry a lot of emotional baggage for a long time. But relatively recently, I came to the realization that the insult was technically correct. If my parents had known better and taken me to a doctor, they would have likely learned that I fit the criteria for developmental motor coordination disorder. My motor skills were (and still are) “retarded”. If everyone had known that I actually had a good reason for acting “retarded”, the teasing probably wouldn’t have happened. Or, at the very least, there would have been more sympathy for me when I expressed hurt over it.
The other day, a coworker laughed at the way I was gesturing while telling a story and told me I looked “flickted”–a word that is more or less equivalent to “retarded”. I thought I had long recovered from my childhood bullying days, and yet all that ancient hurt came back and put me in a sad mood for the rest of the day.
I’m not gonna say I would never ever use the word. But there are so many other insults in the dictionary that don’t press my buttons, so I’m just more likely to go with those.