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Thank you, this seems to be roughly what I was looking for! I was thinking there was one that was more phrased along the lines of "normally squicky thing is fine for the characters because the author wants it to be" but this is close enough, I think... I'm probably just thinking of something from some other site.
Update: Managed to personally locate also "Casual Kink," seems to be an intersection of Author Appeal, Casual Kink and Conveniently Common Kink, maybe? Before I started looking I would've sworn there was a page that specific though...
Perhaps the more general Rule of Sexy could cover those sorts of cases. Where the characters don't share the author's fetishes (so Conveniently Common Kink doesn't apply) but they act out-of-character so fetishy scenarios can play out.
something weird and fetish-y happens, and characters would be expected to react negatively because most people would, but go along with it because the author wants to see those things happen and therefore everyone either shares their fetish or doesn't see anything kinky with whatever's going on.
Not specifically a negative trope, if that's what the audience is there to see. I'd expect to see it as a sub-trope of "Author Appeal" or "Fanservice" but can't find it in either place? I swear I saw a page for it once, years ago, on another computer...