@HighNetGirth
Another very specific African-American term that has been picked up and misused to the point of being meaningless. Like 'woke' (now perjorative) and many others.
It did not start out as a term to use to dismiss women. It was about certain behaviours by white women (usually, but also men) with some status to browbeat and threaten black Americans out of doing their jobs or standing up for themselves.
"Karen" itself is not a "very specific African-American term", though. This is a false narrative, and one which many believe is intentionally constructed and pushed by anti-woman activists with the negative impact to the US black community as acceptable collateral damage.
In black culture in the US, it's very common to use a person's name to reference something that person is known for, and then it gets picked up by others who may not know that person. This practice pre-dates the internet, but once the internet came into play the individual names would be used far more widely.
When consciousness was being raised among the general population in the US about racist police brutality, people who "called the cops" on black citizens for trivial reasons or no reason came under a lot of scrutiny. We saw names like "Permit Patty" and "BBQ Becky" go viral because people were talking about a specific incident before the name of the perpetrator was known or made public.
"Karen", though, went viral around the same time for a different reason which has nothing to do with the US black community (or communities). It comes from a white boy who started a page on Reddit called "/r/fuckyoukaren". He said that Karen was his ex-wife and detailed how she had hurt him/screwed him over. He invited others to rail against "Karen", which, given the demographics and focus of Reddit, included a LOT of sexual violence. It later turned out this was a teenager, so probably a fake story about the ex-wife. The page is still up if anyone wants to look.
Anyway, racists picked this up and blamed the sexist term "Karen" on the US black community, specifically black women. I understand it's also ageist and classist in a UK context, but at this point I'd mainly consider use of the term an example of anti-black racism.
And of course it's very "Karen" to point out the racist, sexist truth about "Karen". Damned if you do and damned if you don't - always guilty. That's how racism (and sexism) persists and replicates itself.