The "R" word: Retarded.
According to Merriam-Webster, it is "sometimes offensive." It means "slow or limited in intellectual or emotional development or academic progress."
If you google the word, you will find search results giving the actual definition and the slang definition. You will find synonyms. And you will find results explaining why this word is outdated and offensive.
When I was in the 7th grade, one of the math teachers made all of her students use the word "fluffy" instead of the "R" word. Because in middle school it made you cool if you called something or someone retarded. But instead of teaching her students to find bigger, better, less offensive words, this teacher taught her students to use a meaningless substitute. Before long, all the 7th graders were simply replacing the "R" word with "fluffly," as if the original version didn't even exist. "Fluffy" became just as insulting and just as over used.
In high school, one of my best friends was constantly telling people to stop calling everything retarded. I'm not sure when or why she got so passionate about it, but she did, and it stuck with me. I started correcting people on their word choice as well, and I have continued to do so in college.
Recently, I heard an educator say the "R" word. An educator, at a grade school, openly said "retarded" in conversation with me. This person was not referring to any student, but to an issue completely unrelated to school. It doesn't really matter though, because an educator should know better. I was shocked, but I didn't say anything. I breezed right through that conversation and pretended I never heard it.
I shouldn't have done that. I could have said "Maybe that's not the best choice of words," "I would appreciate if you didn't use that word around me," or "that word is a bit strong." I could have even prefaced it with "I don't mean to be rude but..."
I have heard people argue that the "R" word is okay because they can't be bothered to be politically correct all the time. If you're one of those people, that's bull s*** and you know it. This word, which was used to classify people who learn a little differently, is NEVER an acceptable thing to say.
So I have a challenge for you. Next time someone you know says that something is retarded, ask them not to use that language. Explain to them why this term is offensive and unacceptable. Be polite, don't be polite, but get your point across. Challenge yourself, and challenge them, to make it clear that this language is completely unacceptable.