use "car wash", or "fast food", but insist on using archaic terms when talking about blacks.
"Murzyn" isn't an archaic term or it is as archaic (slightly less, in fact) as other terms of the Polish language. What's the point in changing terms in Polish into more modern ones, pray tell ! Is it common practice in the English language to constantly "modernize" its vocabulary?
I hear "fast food" very often (and it is declined), but I never hear "car wash" instead of "myjnia" in everyday speech. Perhaps the reason is that we do not have a good counterpart for "fast food" just as we don't have such one for "weekend". The other reason is that :"fast food" is handy and easily declineable, e.g. "idę do fast foodu" rather than "idę do baru szybkiej obsługi" which would be awful and would mean a slightly different thing. For "junk food", I typically hear "śmieciowe jedzenie".
I cannot imagine anyone saying "musze jechać do car washa" which would sound idiotic, so it has never been used in speech which doesn't exclude instances where some idiots would express themselves that way. It also doesn't exclude banners displaying the name of an enterprise, but that's a different story.
From my school days, I remember Polish the famous Polish cabaret actress Hanka Bielicka exclaiming to a group of us, primary school pupils asking her for an autograph at some backstage corridor: "Ciemno tu jak u Murzyna w dupie!" while reaching out for her handbag to take out a pile of photographs so as to write a dedication on them for everyone. If it were a Shakespeare theatre, I'm sure she would have exclaimed "Mehr Licht!" ...Hanka Bielicka