Then one Sunday we were doing our typical "have lunch with the mother-in-law" and I wanted to compliment her on the food, and I ended by saying a very typical expression, "buen provecho" which is similar to the French "bon appetit" and has no real equivalent in English, except maybe "enjoy your meal." However, I got the expression mixed up with another I had only heard but not really understood. I said "Que le aproveche." Which sounded like "buen provecho" to me. Now when I saw the looks on my wife's and mother-in-law's faces, I did not understand what could have gone wrong. The rest of the meal they spoke among each other, and I laid low. Later, when my wife asked me, "How could you say that to my mother?" I said I was innocent, but had a hard time convincing her that I really did not know what I had said that could have upset her so.
It turns out "Que le aproveche" is used when someone takes something from you, and you disdainfully acknowledge that you cannot get it back. It is kind of like "sour grapes", something that my wife assumed I understood because of my competency in Spanish.
However, this humbling experience also showed me that I still had quite a lot to learn about Spanish. And what I had to learn were the expressions and sayings, those idiomatic bits of language, which are handed down from heart to heart, among family and friends, and are very hard to transmit otherwise.