On the internet, not in person? Probably never. Too hard to figure out your tone.

In person? Just depends on your audience I’d guess, my actual gay friends don’t mind being called gay, or queer, or jokes about meaner words when they are meant in a gentle and friendly way, they know me and I know them so we know how to communicate. I don’t find the words useful in other contexts, really only use them to describe a person’s sexuality.

With regard to things not people? Some of the “slur” words still work. I regularly retard my sourdough bread by putting it in the fridge for a day or two, the dough is retarded, slowed down.