I once got into real trouble when trying to explain what “Foot in Mouth Disease” means. They thought I meant they were stupid – which I didn’t, and got really aggressive (they were drunk at the time). I hope they now know how silly they were.

Basically it can be used to describe someone who often says the wrong thing, it’s a play on “Foot and Mouth Disease”. There’s even a “Foot in Mouth Award”, which is awarded each year by the British Plain English Campaign for “a baffling comment by a public figure”.

Here’s a nice little example:-

Thanks to Chewks