Mettre les pieds dans le plat
[meh treu lay pyay da(n) leu pla
To mess up, to speak with excessive candor, to discuss something inappropriate
To put one's feet in the dish
You can't help but notice the similarity between the French expression mettre les pieds dans le plat
and the English "to put one's foot in one's mouth," but they don't mean quite the same thing. The French expression means to bring up a delicate subject without any delicacy at all, or to discuss a topic that everyone else is avoiding. This is probably not embarrassing to the speaker, who just wants to talk about that subject (even if that means unintentionally embarrassing everyone else in the room).
The English expression, however, definitely implies embarrassment on the part of the speaker, since it means that you've just committed a social blunder by saying just about anything you shouldn't have, possibly about something that is - was - a secret (such as the person you're talking to getting fired, or you knowing about someone's extra-marital affair). This would probably be translated by something generic like faire une gaffe
Je parle très franchement - je mets souvent les pieds dans le plat.
I speak very frankly - often too frankly.
Oh là là, tu as bien mis les pieds dans le plat, là !
Oh dear, you messed up there!