When you'd catch someone not washing their hands after dirtying them, you could for instance say "Eh, les lavabos c'est pas fait pour les chiens !", qui basically means that these things were built for use by humans, not dogs, and one should therefore use them... :^^;:
I was actually looking for a direct English translation earlier and couldn't find it, so it's definitely a French peculiarity I guess...
Just like people looked at me strangely when I told them "J'te dirai quoi" (direct translation: "I'll tell you what", actual meaning: "I'll tell you (later) (the outcome of what we just discussed)"), and found out, years later when watching a movie, that it was actually something only the French from the North would say.