The chick who is opposed to the word retarded uses the following analogy:
Imagine your name is Kelly, and one day, people decided to use the word "Kelly" to mean "gross." "Yuck! This food tastes so Kelly!" Wouldn't you want them to stop using your name like that?
Wow, I never thought of it like that. And, like, imagine your name was Rob, and one day, people decided to use the word "Rob" to mean "steal from." "Hey, let's go rob that liquor store!"
Okay, that's not the best example. But imagine your name is Retarded, and one day, people decided to start calling you Kelly. And they're like, "Hey, Kelly, let's go retarded that liquor store." And you're like, "What? I'm completely lost." And they're like, "That's because YOU'RE RETARDED, KELLY."
Hurts, doesn't it?