verb/sə mɛ.tʁə lə dwa dɑ̃ l‿œj/
to be much mistaken, to bark up the wrong tree, to delude oneself, to need one's head examined, to have another think coming
“Si tu crois que je vais t'aider à faire un truc pareil, tu te mets le doigt dans l'œil.” — If you think I'm going to help you with that sort of thing, you're mistaken.
Synonyms: se fourrer le doigt dans l'œil