This reminds me of a much more reasonable bad teacher from my childhood, which I still remember as unfair

We had been learning the vowels, which in one thing were listed as a, e, i, o, u, and sometimes y, among others with the just the five most common ones

So days later when we had a quiz my answer to which letters are vowels was a, e, i, o, u, and sometimes y. I got a red x, with “and sometimes y” crossed out. I don’t think we were given points but it felt like zero points.