I found my post:
Origin of Karen.
It's first ingredient was the Switch's Karen, a big meme in 2016.
www.polygon.com/2016/10/25/13403924/nintendo-switch-karen-meme-reveal-video
To male video gamers, Karen turned into the manifestation of that friend that forces you into situations you don't want to be in. "Oh great Karen brought her switch again". It eventually culminated in "Fuck you Karen" and the meme lost any link to its origin.
It's second main ingredient was the "Talk to the manager" woman.
We can see that the phrases like "Hell naw, Karen" and "goddamit, Karen" were in use in 2017, but they had not, at this point, merged with the haircut.
www.facebook.com/MedievalReact/posts/god-damnit-karen-i-dont-want-to-know-about-how-your-husband-cheated-on-you-with-/1930731887252301/
At the beginning of 2018, Karen is not seen to have any kind of racial angle.
www.newstatesman.com/science-tech/internet/2018/01/karen-sharon-becky-and-chad-how-it-feels-when-your-name-becomes-meme
“Perhaps this type of [middle-aged, white] woman is considered an acceptable butt for jokes about annoying women because she’s ‘generic’, there’s no race or class angle,” she says. As for why middle-aged white men feature less often in these jokes (Barry is perhaps the only middle-aged male name consistently memed), Cameron says male names carry less social information because parents’ choices tend to be more stable over time. She also notes sexism could be a factor.
This SNL skit seems to be where it took on the "racially insensitive" aspect:
www.youtube.com/watch?v=lLkmZzcedhs
But it is generally credited by the reddit community to have reached notoriety from the the reddit /r/fuckyoukaren - by a man who posted repeatedly and bitterly about his ex-wife Karen. The reddit is still going, but here's a thread from the same year discussing its contribution to the meme.
www.reddit.com/r/OutOfTheLoop/comments/7lz4ar/what_is_this_fuck_you_karen_thing/