Neither French nor English native speaker. Here are my two cents.

Face (En) and Fesse (Fr). The latter means buttock in French.

Preservative (En) and Préservatif (Fr). The latter means condom in French. Food preservative is conservateur in French.

See also here:

https://www.talkinfrench.com/french-translation-pronunciation-mistakes/

For developers, the word string is often a source of jokes because in French un string is a thong (we’d rather use the feminine une string when talking about the code thing, though). But worst than developers joking about it, it’s when non-developers are passing by and hear you talking about strings like it’s normal conversation.

And there are all the bit things, since the French word bite (pronounced a bit like the English word beat) is a dick, a cock. So when talking about game consoles, especially with someone not really into it, bit sounds immediately like you’re talking about a dick. So if you say a console has 16 bits, one could answer (as a joke) that it is a lot of… dicks. And you have jokes like: “Avec la nouvelle Super Nintendo, mettez 32 bits entre les mains de vos enfants”, which means: “With the new Super Nes, put 32 bits (dicks) in the hands of your children”.