The expression âSacre Bleuâ actually has a very long and storied history. Beginning in the early 1330s, it has itâs roots in Thomas Stansford, a dye salesman that used thistles and some sort of lye to produce a radiant blue dye.
So blue and enchanting was this dye that he named it âSacred Blueâ but they discovered that the actually pigment in the end was toxic. Not very, but it would in high dozes be diuretic and laxative.
Of course, no one wants the shits from their blanket. But, the soon starting 100 year war would see another use for the dye, as a sort of... psychological warfare against the french. Thomas was commissioned by the English to engage with trade with the French in order to have their radiantly blue uniforms slowly and annoyingly poison them, keeping their armies sick.
Later on, this was all revealed from the french and the term âsacred blueâ was quickly adapted as an exclamation of disgusting. Of course, it was changed to fit with how French works.
So there you go. The more you know