The Rule of Thumb
Thou shall not beat your wife with a stick thicker than your thumb
I got this from my husband. (I did!)
Yeah, I've seen it: all the fuss by historians, lawyers, psychologists,
feminists, ethymologists et cetera explaining that the phrase
was not coined expressly for the purpose of alluding to wife beating.
I don't think it was.
But I think that's beside the point, isn't it? Why, the point is that the phrase fits.