You're asking all the right questions.
Lately, it seems that the only thing that matters is passing the vibe check.
Things that surprisingly pass the vibe check:
* "long time no see" or "no can do" -- making fun of broken English (particularly Chinese and Native American)
* "got gypped" -- clearly insulting toward gypsies
* criticism from the "peanut gallery" -- that's a reference to poor seating for black people during the Vaudeville era, which is super racist by any standard
Things that unsurprisingly don't pass the vibe check but should if people were more educated:
* "jimmies" for sprinkles has a pop culture reputation for being racist and people have corrected me for saying it, but actually ice cream sprinkles were just invented by a guy named James
* "niggardly" shares no root with its racist homophone
* "那个" is a filler word that chinese speakers need to be careful with because of the same racist homophone
I get that language is always evolving and the vibe check does matter to lots of people, so I try to accommodate the sensibilities of the masses.
I know that "niggardly" is so uncommon these days that it practically is a racist dog whistle (though it really shouldn't be), so I wouldn't use it in daily speech.
But I also think it would be a shame if all the interesting turns of phrase that have stuck around over the years are intentionally censored and removed until we have nothing but bland language without metaphor or history or anything that could possibly cause offense.
"Opening the kimono" is certainly not a phrase worth censoring. I think you could make a good faith argument that trying to censor it is actually a reflection of racist and sexist American stereotypes about Japanese people.