My little girl has recently taken to comment on the quality of food, distinguishing between “bon” (good) and “pas bon” (not good). So the other day, I asked my little girl if her yoghurt was good: “Ist der Joghurt lecker?”
This is the reply I got: “C’est pas pas bon.”

Now let’s see: “not not good” obviously means “good”, but how did she get there?
Here’s my theory: to her, “pas bon” is not composed of the negation “pas” and the adjective “bon”, but is a word that stands by itself, maybe “pabon” that means “bad”. So a more accurate translation of “pas pas bon” would be “not bad”.