Best wishes to all people in France on Bastille Day!
In honour of the day, what is your favourite French word or phrase which is in common usage in English?
Three that come to mind quickly are: joie de vivre, je ne sais pas, and au contraire.
I think "je ne sais quoi" has a certain je ne sais quoi about it.
If we're stretching it to cognates, I like that "toilet" means "towelette" in French. Though I'm pretty sure I'd prefer a moist towelette to a moist toilet.