If you've spent any amount of time on the internet in the past year or two, you've heard someone be described as a "Karen." The slang term originated in the black community as a way to jokingly describe a particular type of entitled white woman with a bad haircut and a tendency to write negative Yelp reviews. It's not actually about women literally named "Karen," although there is likely to be a some overlap.
Dictionary.com sums it up well:
Karen is a mocking slang term for an entitled, obnoxious, middle-aged white woman. Especially as featured in memes, Karen is generally stereotyped as having a blonde bob haircut, asking to speak to retail and restaurant managers to voice complaints or make demands, and being a nagging, often divorced mother from Generation X.