It’s used in many circles as a “polite” synonym for removed—a slur for people with Down Syndrome.

If you’re going to dehumanize a person, I think it’s best to call them something that’s entirely unhuman (e.g. demon, ghoul, etc.) rather than something human-like (e.g. orc, ape, etc.). Human-adjacent words tend to get reappropriated as a “polite” way of saying (r-word). I recommend avoiding that trap entirely.

Edit: the slur filter is smarter than I am! It removed that one, too! You can guess what word it was, though.