- Using words that are commonly used to refer to particular groups as insults (turning “mentally handicapped” into a pejorative, for example);
- Repeating words (and their derivatives) that marginalised people have regularly experienced as abuse (eg “retard” or “retarded”).
Unless you don’t give a damn about hurting people because it makes you feel all big and rebellious and tough to further grind down the already marginalised.
I do, and it doesn’t, which is why although I have previously used the word “retarded” on the grounds that (a) it’s already pejorative, (b) nobody uses it to identify themselves and (c) it has a specific meaning that has nothing to do with human beings (it means “slowed”, and we use it to describe objects with particular properties), I am going to stop. Because regardless of what I mean by it, it is used as a term of abuse directed at people with particular disabilities, for example, and thus hearing it again unnecessarily and cruelly compounds the injuries previously suffered.
And I’ve got some ideas for other names to use as synonyms for “stupid”, anyway.