se mettre le doigt dans l'œil

You use it when someone is delusional or overly optimistic. You can use it for yourself too. Simply conjugate the verb se mettre. For example: Je me mets le doigt dans l'œil. It works perfectly in the present tense. You can also use it in the past. Use it when a friend thinks they won the lottery. Use it when a coworker thinks the boss is giving everyone a raise.

Use it during casual debates with friends. It is great for lighthearted arguments. Use it when someone makes a wild assumption. Imagine you are at a restaurant. Your friend thinks the bill will be cheap. You know it is a five-star place. You tell them they are putting their finger in their eye. It is perfect for texting when someone sends a 'fact' that is actually fake news.

Do not use this in a very formal job interview. It is a bit too colorful for a CEO. Avoid using it if someone is genuinely grieving or in a serious crisis. It can sound a bit mocking. If the mistake is life-altering and tragic, stay away. Also, do not use it literally. If someone actually has something in their eye, use avoir quelque chose dans l'œil instead.

This expression dates back to the 19th century. The idea is that if you put your finger in your eye, you go blind. If you are blind, you cannot see the truth. It is a very physical way to describe a mental error. French people love using body parts to describe emotions or mistakes. It feels very visceral and 'French'. There is even a longer version: se mettre le doigt dans l'œil jusqu'au coude. That means you are wrong up to your elbow!

The most famous variation is se mettre le doigt dans l'œil jusqu'au coude. This implies you are spectacularly wrong. It adds a layer of humor. Another variation is simply saying Tu te mets le doigt dans l'œil. Sometimes, people just make a gesture. They might pull down their lower eyelid with a finger. This is a silent way of saying 'I don't believe you' or 'You're wrong'. It is a classic Gallic shrug in finger form.