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 ...
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: