A “Karen” is a nosy, holier-than-thou type who asks to see the manager or raises a public fuss when someone considered “lower” doesn’t jump to every command or agree with their point of view.
They often will post follow-up social media complaints, &/or nasty reviews in an attempt to gain sympathy and (hopefully) get the perceived offender fired or shunned.
Karens can be female or male and any color, shape or size, many tend to lean liberal and have “Hate Has No Home Here” signs prominently displayed on their front lawns.