French phrase
Vous vous trompez.
Meaning
You're mistaken.
When to use it
Indicates that someone's view is incorrect. It can be a calm correction, though delivery may make it sound accusatory.
Example dialogue
Vous affirmez que c'est moi qui ai pris le sac ?
Are you saying that I was the one who took the bag?
Vous vous trompez. Ce n'est pas moi.
You're mistaken. It wasn't me.