Green’s Dictionary of Slang

(orig. US) an over-privileged (upper-)middle-class woman, stereotyped as invariably demanding to ‘see the manager’ when unhappy with service, e.g. in a supermarket, by a person of colour.

2018		Urban Dict. 13 Mar. 🌐 karen typically never a name given to a baby but somehow karen always turns up asking to see the manager.
2020		Guardian 13 Apr. 🌐 ‘Karen’ is commonly used in the US to refer to a strident middle-class white woman who talks down to people of colour, usually in serving-staff positions.
2021		Betoota-isms 69: Karen [...] 1. An entitled, white middle-class woman displaying obnoxious behaviour in public, particularly towards retail employees 2. A pejorative term used to profile a deep-Gen-X or shallow-Boomer woman who carries a sense of entitlement beyond the scope of what is normal.
2022		I. Fitzgerald Dirtbag, Massachusetts 129: The Karen (pronounced ka-ren, as opposed to the name of someone demanding to speak to your manager.