Mine is that at my age (barely made it into Gen Z on the old end) I just found out today that a Bo Weevil is an insect (beetle) and not some kind of mole or similar rodent.
“Cake” in “let them eat cake” is “brioche”. I had thought that cake meant cheap chemically leavened bread-ish, but it actually was an out of touch elite being genuinely confused about bread shortages, not someone callously suggesting the peasants eat shittier food.
Also it probably wasn’t Marie Antoinette.