@mae retardation is not a clinical term anymore, it's not a medical condition. people use it as a mild insult of someone's mental faculties, in the same way "idiot" is used today versus its historical usage.
this joke does not target any particular group with mental disabilities. in contrast, I'd never post a joke about downies or people on ASD spectrum.
banning words is authoriatarian and will just result in other words used to the same affect. also what is and what is not a "slur" is arbitrary, and largely to do with ingroup/outgroup dynamics Consider "Jap", a short hand for "Japanese", because of WW2 this is considered a slur because the context was for othering, but "Brit" as a shortened version of "British" is largely ok, because there is no need for othering there (Unless you're Irish maybe ;) ) as usual, context is key. @kaia
@kaia it's not a mild insult, it's a serious ableistic slur. it's seriously offensive and derogatory. if you can't see how that's an issue that's your thing, but please think about it for a minute before you do. you probably don't like reading the t-slur either even though it's not a clinical term.
"downie" is another similar term by the way... it's dehumanizing and awful language.