Interesting thread.
To those asking why give this "type" a name, it's just something that humankind has always done. There are endless examples throughout the years:
Smart Alec
Clever Dick
a proper Charlie
spotty Herbert
a right Wally
hooray Henry
Billy no-mates
Nancy boy
a big Jessie
Fagash Lil
Anytime Annie
and none intended as a compliment. It's not personal to people of those names, although I'm sure it's not pleasant if people direct it to you as a "joke". Just ask anyone who got "Who the fuck is Alice?" whenever they gave their name (usually by men who thought they were hilarious). It passes.
The "Karen" type is very specific, according to DS (a manager) who works at a well-known fast food outlet to fund uni. Yes, they ask for the manager but usually to insult, swear at, and make a fuss over something incredibly trivial. He's regularly sworn at, had a tray of food thrown at him because the fries weren't hot enough, and been physically attacked because the delivery workers weren't unloading quickly enough and she wanted her salad instantly.
I asked him what they call the men who do this, and he said "Nothing, because men rarely ask for the manager". He reckons he has dealt with one man in his year as a manager, but countless dozens of women. He also reckons that it's not because they are women, as older women tend to be generally polite, and younger women tend to be more sympathetic as they have often worked in "unskilled" customer-facing roles themselves and have been on the receiving end of similar abuse. But middle-aged "Karen" complains, because she expects that she and her children (they always have children) are treated like royalty, because they're worth it.
Not all middle-aged women are Karens, he said, but they can spot them as soon as they enter the restaurant or drive-through.
I showed DS the "Karen" thread from a few days ago, and when he saw the post with the haircuts he said, "That's her! They all look exactly like that!". I guess stereotypes come about for a reason.