I don't remember if this has been mentioned before, but the term "Karen" is so overused that it has become meaningless. It originally referred to a person that was a busybody and made a federal case out of every little thing. However, I've noticed it's now just being used as a mindless, catch-all insult online when someone simply disagrees with you, even if your post has nothing to do with being meddling or vindictive.
Person 1: "I like the new model of this car."
Person 2: "It's ok, but I'm not a fan of the new console design."
Person 3 (to Person 2): "Ok, Karen."
Maybe its recent (and relative) overuse (and even poor application of its use) has diluted its punch, but it’s also filled a longstanding void in everyday vernacular for which there was already a gendered equivalent for men (see below).
In my circles, there remain a couple of select folks we know of in our local community, for which no other word — for worse or better — more fittingly describes who those folks are and the levels of harassment (and even stochastic violence) they are known to invoke toward others who not only unsettle them (often, directing their “karening” toward others who are, generally, living a better life than they are and, thus, why they’ve earned that ignoble title), but also look down upon as inferior/subordinate to their own (perceived) station.
tl;dr: Sometimes new slang sticks because the slang works and no better alternative is in wide use.
“Karen”, at least for me, is the feminine of the masculine “Dick” (as in, “Van Patten”, “York”, “Sargent”, etc.), but the paths of those earning those distinctions run pretty different.
The former usually does so by summoning authority figures (e.g., “managers”, “supervisors”, the police, whatever) to bend others to their own will and/or whims. The latter, usually pretty aggressive, tends to take matters into their own (overtly violent) hands. (A common example: some dude in a truck and road raging all over the place.)
“Boomer” almost sounds like some sort of nautical sailing term.
“How say you, Donald Fagen?”
Isn’t that also what they call submarines that carry nuclear missiles.
Whoa. (!!!)