Depending on the company you keep,of course you're not literally going to be laughed out of the room. But be sure there's some internal laughing.
Still good to know.
Do you feel like Parisian French is really the same as English as spoken 400-1000 years ago, though? Don't people in Paris speak Parisian French right now? Sure, if someone walked up to me and said "Doubt thou the stars are fire, Doubt that the sun doth move. Doubt truth to be a liar, But never doubt I love." that might seem a bit odd. But if someone who learned English in Britain calls french fries "chips" and potato chips "crisps" I'm not going to have to bite my own cheek to stifle a laugh. That's just so unbelievably smug.