Well, now we've covered les politesses in previous posts, let's move on the the real reason it's fun to learn a foreign language. It's because you want to know the rude words, bien sûr. The first rude word that everyone learns in French is merde. It's so well-known that you probably encountered in your High School French textbook, and disappointingly, it's just not that rude in France. Everybody, including our 90+ year old neighbour uses it (when she drops her walking stick), although nicely brought up people do disapprove of its indiscriminate use in every conversation.
neighbour Pierre-Yves would say
Zut ! and zut alors ! are exclamations I learnt in school French lessons. They were in the text books, so I assumed they must be seriously uncool and no one really used them, even 30 years ago. But I had a conversation with our stone mason recently that went:
Stone Mason: Nous avons besoin du dictionnaire !
Me: Bah oui, mais je l'ai oublié...
Stone Mason: Zut !
If you are worried that merde and zut might be too impolite for the company you are in, but you need an expletive, you can use mince ! (pronounced more like 'manse'). It actually means 'slender', but can be used the same way that in English one substitutes 'sugar' for a 'harder' word.