I guess it's fair to say that when you're learning a new language in a new country, it's natural to try to add some phrases to your vocabulary. I think the first French phrase I clung to was "n'importe quoi," which can be thrown out there like "Whatever!" Probably the the one I use the most frequently is adding on the word "quoi" (literally means "what") at the end of the sentence, which is the equivalent of the American overuse of the word "like," but like its American counterpart, should, like, be used, like, totally like sparingly.
My friend kyliemac often says that her favorite French phrase is "ferme ta boîte à camembert," which literally means "close your camembert box" (camembert being a tasty kind of French cheese), but really means "shut yer piehole" in kidspeak. Kylie hears this a lot because she is regularly in the presence of French kids, but as I am not, I had never heard this phrase in use before.
Well, before last night, that is. I was all comfy on the couch with Shrek (dubbed in French) playing on the tv but mostly paying attention to my knitting, when I heard it, and it happened so fast I nearly missed it, but no, there was L'âne (Donkey) telling Shrek to "ferme ta boîte à camembert et écoute-moi!" (Shut up and listen to me!) I got so excited because a) this normally would have gone right over my head and b) I finally heard kylie's favorite phrase! Yay!