Here is a picture of Donald Trump someone created online. My apologies for not finding the creator, to provide proper credit:
Why it is a funny picture requires a) knowing that the Supreme Court of the United States recently decided that president Trump cannot hide his tax information, b) knowing that this would obviously create narcissistic rage in our Donald who would therefore scream about it, and c) knowing the online Karen meme.
The Karen meme may have been* created by Black women to describe the type of a White woman who would act in overly entitled and racist ways while dealing with people of color working in customer service, often demanding to see the manager. The Karen of this original meme is a racist middle-aged, middle-class White woman, and the point of the original meme was to draw attention to racist behaviors by White women.
The meme, however, has also taken on a life of its own**, so that is now be used as a general slur about (mostly) White women who do stupid things (such as not wearing the mask against the covid virus) or about (mostly) White women who express controversial opinions.
Returning to the above picture, the joke that we are supposed to get from it is that Trump has now turned into a Karen! The only way we might ever be able to realize that Donald Trump (an extremely powerful, rich, entitled and rude White man) truly is overly entitled is by depicting him as a woman called Karen!
And that, my friends, is sexist***, whatever your opinions of the popularity of this meme.
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* I have not done the necessary research on the very first appearance of this meme. I have also seen someone argue that the first use of the term was by a man berating his ex-wife and that even earlier uses exist.
** The male-centered Reddit discussion site has several large Karen subreddits where people collect their stories about entitled women calling the manager, being racist, or doing something else the posters found irritating or stupid or anger-causing.
These stories are not necessarily sexist in themselves. Many of them describe (alleged) bad behavior by some (usually) White woman, and doing that would be okay if similar subreddits also existed about White men who do stupid things (refuse to wear the covid masks, say), who act in racist ways, or who feel overly entitled and want to see the manager when things aren't to their liking.
Those types of behavior are not less common among White men than among White women. But White men who behave badly are mostly not given a name (Bubba?), and that name is therefore not employed in creating a meme about a large sub-group of people. The only exception I can think of to this rule is "the Florida man" meme, but it is nowhere as widespread as the Karen meme is today.
What all this means is that the individual acts of really stupid or rude or entitled White men are seen as just that: Individuals who are acting like assholes. Here is one example of that. (My apologies for losing the source for this one, too. I blame my illness.) The original didn't give this man a generic name which would create a meme applicable to all White men of his age and general looks out of his behavior.
But that is what seems to be happening to the Karen meme. I have seen a few attributions of a possible Karen status to someone just because of a particular haircut (short and fairly straight) and hair color (blond), even when that person is a stranger who has done nothing Karen-like and is not planning to do anything Karen-like. So one can become a Karen simply because one looks like what someone thinks Karens do!
*** We tend to use most of the -ism terms without thinking of their basic definitions. It can be useful to do so, however. In this particular case the correct way to think about this term is to ask if anything changes in our responses if the only thing we change in some incident is the sex or perceived sex of the culprit while leaving what the individual does intact.