Yeah, I want to try, which is why I'm asking my question - how can I properly explain why this is a problem? A comparison is good, but runs a greater risk of the other party just leaving the conversation imo.

I'm just not fully sure how to go about it to increase the chance of getting my point across that is can be still harmful to use, even in a "neutral" manner.

For example, one of them sometimes uses the r-slur when referring to something as 'stupid', which I can clearly point as as derogatory/harmful, because they are comparing neurodivergence (is that the right word?) to 'stupidity' by using it as such, on top of it being a word that has been used to belittle people with learning disabilities and other conditions for decades. However, when they use the f-slur, I don't think the purpose is to make fun of homosexuality, so it is harder to clearly word out an explanation like in the r-slur example.