Z, does that topic mean anything to you?
I mean, I understand what it means (we have the same "bête comme ses pieds" in French), but as for which reason could motivate you posting a thread with this title and asking this very question to me, I'm afraid no, I have no clue.
I'm listening to an Audio Book, and someone said, "bête comme ses pieds" (well I don't really remember, but what you said sounds good). Then an Australian who was able to translate it, said, "Dumb as my feet?", not knowing what that meant. Then a French person said it was an insult. So, I was checkin' with you to see if that was true. 🙂
Well, it is! I hadn't realized you haven't this idiomatic sentence in English. It's indeed an insult in French. But not something you can throw at the face of someone when you're angry - more something that you can condescendingly say when speaking to someone about someone else that typically isn't here to hear that. Even then it's not super frequent.
Naw, we wouldn't say that in English. We might say dumb as a post, stump, or rock, but nothing to do with feet. 🙂