Clearly a reference to "white savior" Robinson Crusoe's manservant Friday, a highly offensive stereotype of a subservient BIPOC.

Know your hierarchy of oppression. That's sexist. Clearly it would be code for His Girl Friday.

"Girl"? Seriously? Infantilising women is sexist.

It’s a reference to an old movie.

Origin early 17th century (as school slang, in the sense ‘Friday on which an examination is held’). The shopping sense dates from the 1960s and was originally used with reference to congestion created by shoppers; it was later explained as a day when retailers’ accounts went from being ‘in the red’ to ‘in the black’.

I always assumed this was a tongue-in-cheek reference to the 1929 market crash and subsequent events.

Taken to mean “this is going to be a really stressful day”. Probably utterly not at all that though.

The real answer is that financial ledgers used to use black ink for positive numbers and red for negative, hence the terminology "in the red"/"in the black" to mean an enterprise is in debt or profitable. Black Friday was the day of the year where every department store would have so much business that it put them "in the black", even if they had just spent the entire previous part of the year "in the red".

That's a good story, but according to Wikipedia this etymology was invented after the fact and isn't the real origin of the term (which is somewhat obscure.)

...and which pen is used in an accounting ledger at certain times of year is not obscure?

I don't get what you're saying. It's not obscure at all that black ink denotes profits and red ink denotes losses - "in the black" and "in the red" are well-understood English phrases.

All I'm saying is that this particular meaning of black/red doesn't appear to be the origins of the name "black Friday", at least according to Wikipedia, but I really don't care about this enough to investigate any further.