merde
Merde literally means 'shit', and the French use it about as often as English speakers do. Oh merde ! is what slips out when you drop your phone or slide across a wet floor. Être dans la merde means being in deep trouble. It's rude, not shocking: fine with friends, less fine with your future mother-in-law.
Where you'll hear it
Chloé
Attends, je vais venir voir. Il faut peut-être que je te montre.
Wait, I'll come and see. Maybe I need to show you.
Robin
Non, ça va aller. Je vais réessayer.... [quelques minutes plus tard]
No, it's okay. I'll try again.... [a few minutes later]
Robin
Oh merde ! Je viens de glisser sur le carrelage mouillé. Je me suis fait mal au coude.
Oh shit! I just slipped on the wet tiles. I hurt my elbow.
Chloé
Fais attention ! Tu veux que je t'apporte quelque chose ?
Be careful! Do you want me to bring you something?
Listen: merde
How it shows up
Merde, j'ai oublié mes clés !
Damn, I forgot my keys!
Si je rate ce train, je suis dans la merde.
If I miss this train, I'm in deep trouble.
Demain c'est ton examen ? Merde !
Your exam is tomorrow? Break a leg!
Questions people ask
Why do French people say merde to wish good luck?
It's a theatre superstition: bonne chance is supposed to bring bad luck, so actors say merde before going on stage. It has spread to exams and job interviews. The polite answer is a simple merci.
Is merde a bad word in French?
It's a swear word, but a mild one. You'll hear it on TV and from your colleagues. Skip it in formal settings, and if you want the softer version, say mince.