It came to be from more than one thing in the USA.
There was a tv series years ago, I never watched and one of the main characters
was 'Karen'. In my opinion and probably many others, the hair style was awful.
It was a rather popular hair style but I wouldn't dare have my hair cut that way.
It was and is a woman's hair style in which it is cut relatively short, longer on
one side than the other and very very short in the back. Straight hair. Obviously
there was people such as myself that absolutely hated that hair style. I mean, it
was/is a hair style that irks some people like myself. You know how something
makes your skin crawl.....well not that bad but almost. Yep, there are still women
that have that kind of hair style.
So people would some times say 'there goes a Karen' because it was a woman
that had the same hair cut as the actress 'Karen' in the show.
Then the name began to evolve. It became a name for a middle aged white
woman that was belligerent in some way......acting out, causing trouble, very
Now the term 'Karen' is being used more with racism. The video of Amy Cooper
acting out against the black man, many has referred to her as a 'Karen'.
In regards to 'Darren', I don't know. My guess is it is similar to the Karen meme
lately only a rhyme someone came up with. Karen...Darren. So obviously Darren
is another meme for a man acting out.