Mon dieu! Today I made a terrible faux pas.
We were in a boulangerie to buy sandwiches for lunch. Monsieur came in, obviously in a terrible hurry. “Après toi,” I said, even while my brain was screaming at me to use vous, not toi. I know the right word to use, but I was concentrating so hard on avoiding saying toi, it just popped out. He immediately corrected me, to which I said “pardonez-moi” several times. After buying his sandwich he came to explain further, that toi was the wrong word to use, that in the South it is ok to use toi, but in the North we must use vous. And this he explained to me in English, since I’m obviously too dense to understand French. Merdre! Zut alors!