Here comes another one of my little pet peeve rants....
Many years ago, I was in a Crate & Barrel store in Chicago (enough years ago that Crate & Barrel was THE place to shop for young up-and-comers, then called yuppies), and overheard a young couple discussing some kitchen accoutrement. The young man said to his partner:
"I like it. It has a certain je ne sais quois, but I don't know what it is."
(check the link if you also don't know what it is).
There was the incident where I pointed out to someone an amusing use of tempus fugit. He responded with "Right, let the buyer beware!" (again, take a look if you don't know why that's odd, and yes this is Latin, not French)
Today, I received an e-mail post from one of the many marketing groups to which I belong. This particular message was about word use and writing (good writing, one presumes). This message opened with:
"Vitriol is our word du jour this week"
In my house, when I make one of these completely disconnected mis-uses of an idiomatic phrase (English or otherwise), it's usually the subject of hysterical laughter, and not the butt of a bad joke about inability to express myself.
Careful with those non-English idioms!