I'd say that I grew up in a relatively progressive, accepting, and diverse high school and that, for this, I am lucky. I also had the privilege of being involved in my school's Diversity Club and working at a summer camp for disabled young adults. Growing up, and as others grew up around me, I stopped hearing the offensive and disparaging r-word thrown at peers well before high school.
When I came to Fordham I was surprised by how commonplace this word was in the vocabulary of the otherwise great people I met at the school. I have even witnessed a professor use the word in an academic setting. I understand that, while this word is incredibly offensive and my impulse is to think less of those who use it, not everyone was as lucky as I was to have been exposed to the unique set of circumstances that I had which made me realize the affronting nature of the word. For this reason, I would like to explain why you should not use this word, ever.
In the 18th, 19th, and 20th centuries, many developmentally and/or physically disabled individuals were medically labeled "retarded". This word harkens back to a time when the disabled were institutionalized and subsequently abandoned, abused, restricted, starved, beaten, dehumanized, sterilized, raped, and, overall, miserably mistreated. Developments in disability rights are fairly recent and there are several generations alive today who were labeled this word all the way from infancy. For this reason, as well as lack of medical accuracy, the harm of labeling, and the insinuation that a disabled person is simply "stupid", the word is extremely inappropriate to use against or when describing a person with a disability. "Retarded" in this context is a dictionary-defined slur.
A common argument I have heard for why the word can be used is that, because the people who use it are using it towards their able-bodied friends, it, therefore, is not being used against those with disabilities or in a problematic context. I ask this: Is racism not racist when used behind closed doors? The same applies to ableism. The fact that it is an insult to call someone a label of a certain demographic undeniably lowers that group to a position under the one using the word. Stop the subjugation in your day-to-day life and calmly explain to your friends why they should expand their vocabulary instead of resorting to slurs. Allyship is a constant process of allied acts, acts that are uplifting those who are not present and cannot speak for themselves. Speak kindness.