Oh, I took the school's definition as mutually exclusive --- and I assumed the son did as well.

I didn't see how it was not --- and so the line of questioning seemed to be willfully ignorant of that mutual exclusivity.

We have "not ripe" and "ripe" apples. Is this apple "ripe"? But see this part of it here isn't ripe! So it's both ripe and non ripe --- ergo, you were taught wrong to distinguish between ripe and not ripe!

blank stare == (are you really that stupid dad?)