I was concentrating on the pejorative use of the term as relating to criticism of people and/or things. I think its obviously fine to say, for example, "the rotation of the wheel was retarded due to friction".

> Even if you're not sensitive to peoples' feelings about words, one good reason not to use "retarded" is that it makes you sound like a playground bully.

In not wanting to sound like a playground bully aren't exhibiting sensitivity to peoples' feelings?