You're not imagining it.

I've seen it (and many other ableist slurs) used far too often, especially for a site that is generally supposed to be more left leaning (which tbf isn't saying much when it comes to combatting ableism because we seem to have very few true allies) but is also full of tech-bros, who love punching down at others based on perceived intelligence, and who also have quite a lot of crossover with 4chan type cesspits, so sadly it isn't unexpected.

I call it out it when I see it, and generally block and report, but what I find most frustrating is that mods throughout lemmy/fediverse (again, even on the most supposedly left leaning instances like lemmy.ml) just ignore the reports and don't remove the comments (I know people are busy, I don't expect instant action, I give it a week or two in general before I check the modlog).
I've had to block several large communities, most that I'm actually interested in (mostly tech and science related, again, places where people love feeling superior based on perceived intelligence), because I get the message - making people like me feel safe and included isn't a priority in those spaces, so I refuse to occupy them.

Whether the privileged group accept it or not, that is the result of using slurs - making already marginalised people feel unwelcome and excluded.

And when they tell me not to be so easily offended, I link this (or maybe this or this) with the full knowledge that they will probably never read it, but with the hope that someone else might, and that it might make them reconsider their use of certain words (though I don't hold my breath in anticipation of society at large giving a shit).