French and English share quite a few false friends, that is words either spelled similarity or that sound the same, but with very different meanings. Here's a few.
Liberal/Liberal (US): Let's start with politics. In France a liberal supports free markets and free markets solutions to economic problems. In the US a liberal supports a balance between individual liberty and social justice freedom and that the state can and should try to fix economic problems.
In other words a liberal in France is on the right and a liberal in the US is on the left.
Préservatif/Preservative: These false friends do have similar meanings in both languages. Just that a préservatif (birth control) is to preserve a woman from getting pregnant and a preservative preserves food.
Cross/Cross: A cross in French is a cross-country race, possibly where the French word came from. The French very much like to shorten English words they use as in email = mail - see below. A cross is croix in French.
Control/Control: Anyone that's taught English in France knows this one. In French the verb control means to inspect/check and in English it means to have power over.
J'en ai marre/Johnny Marr: These sound the same. Johnny Marr, the British rocker and j'en ai marre, I'm fed up! The latter the French say a lot :).
Fart/Fart: This one can leave the English speaker red faced explaining what a fart is! In French fart means to wax as in Fartez mes ski, SVP. - Wax my skis please. FYI - the French for fart is pet (n) and péter (v).
Phoque/Fuck: Another one that can leave an English speaker red faced. The French for seal - Phoque sounds a lot like fuck.
Blouse/Blouse: Back to the benign, blouse (pronounced blues in French) means smock in English. In French a blouse is a Chemisier.
Mail/Mail: In France email is mostly know as 'mail', the official translation of email is courriel, but few use it. So next time a French person tells you 'Je te fais un mail', their mail is email and not postal mail. So you're better off using UK English here, 'I'll send it in the post' and not 'I'll send it in the mail'. Just to make things clear.
Journée/Journey: Another one the French misuse when speaking English. Journée in French means day, as in Quelle journée ! - What a day. The French for journey is voyage.