@alidan
Yeah,
maybe ( can't comment on that, not a US denizern ) in the US Karen might be becoming a mainstream word ... but the US have not even 20% of the people that have english as first language. And this is not even talking about people ( like myself ) that do not have english as first language but that are reasonably fluent on it ... ( P.S I actually prefer english TL of manga than on my native language because the translators tend to not be as good as that ... but that is a rant for other day )
And that was my point. If you were translating for Redditland, Karen would be A-OK. If you were only translating for the US market, Karen might be ( or not ) aceptable without any other caveats. But for a world audience, that is what you get when you post a translation online ... not good. Atleast without a TL note., I mean.
The target audience in the end is the main decider in here ... and in the end, when you make a TL to put online, you're translating to
everyone in the world that can read that language, not only your country and your socio-economical strata, gender,
etc ... You can't assume they will know your local slang, no matter how widespread it is where you live or in the social enviroment you move in. It is a whole diferent issue from a book translation or scientific papers translations , where audiences are more constricted and where it is expected that you use less generic wording. In fact it might be required that you know and use local slang or specific terminology
On the "weird costumer" thing ... again, from the little Japanese I know ( definitely not fluent in it ... in fact, I'm barely able to grasp the general idea most of the times ), the idea I get from the original text ( anyone more fluent than me feel free to correct ) is that the term used is more in line of those Japanese housewifes in the eternal search for a bargain that we see in flocks in so many manga and anime than on any know-it-all and demand-the-manager attitudes that the term Karen as used in the US memesphere calls for. So, weird costumer might unfortunately be too generic, but alteast is more accurate ... :/