Tu te trompes, et tu as tort.
tew tuh traw pay tew ah tore. Click below to hear this.
You’re wrong, and you’re wrong.
Another “Huh?” moment! These are so much fun.
If you learned your French a long time ago, as I did, and in a traditional classroom–as I also did–you learned that Tu as raison means You are right, and Tu as tort means You are wrong. What you may not have learned, or not learned until later, is that there is a nuance: Tu as tort means that you are acting wrongfully, whether it’s immorally, unethically, or just plain contrary to common sense.
You need a different expression to say that someone is making a mistake: declaring incorrect information, for instance. One way is to say Tu te trompes, which literally means You are deceiving yourself. This expression acknowledges that when we make a mistake, it is usually in good faith. You forgot the correct information, or made an incorrect assumption, or got confused. You did not set out to lie.
Once in a while, however, it happens that believing that your incorrect information is in fact true (Tu te trompes) results in making an inappropriate decision about how to act (Tu as tort). Assuming that your little brother was the one who broke your toy train could lead you to beat him up–not an appropriate way to handle the situation. Your assumption that he was in the wrong may put you in the wrong, instead.
And that’s when people will start saying of you: Il/Elle a tous les torts de son côté (The fault is entirely on his/her side).