Ok, I see now what you meant. Yes, I get why Karen was chosen as a representative of that demographic.
Yes, it is unfair. It would bother me less if a generic term was used rather than a specific name. However, it still conveys sexism to me, because I feel women are judged differently than men on the same type of behavior. And it seems older women especially, are often marginalized in society. JMHO.
I’ve never heard Kevin or any other male name used for this type of person, but I’d be against that as well. You can brush it off as a joke, but really it’s mean-spirited and childish name-calling.