Wow. Shows how a folk etymology can prop up some unfounded confidence.
I had always been certain “Sacré bleu” best corresponded with the English “my heavens!” I thought bleu (blue) stood in for “sky” (as in the wild blue yonder of the USAF song). So, to my reasoning, “Sacred Blue” = “Heaven”.
My confidence in this interpretation was strengthened by the knowledge that French (as well as some other languages) uses the same word for both “sky” and “heaven” (“ciel”).
I had always thought of it as mild, polite company, interjection or exclamation. I had never thought of it as a heavy expletive or swear word.
Ignorance fought. Thanks.