Comment from my PE teacher (who taught other subjects too, but not to me) when I was 12, in an otherwise good report:
He has wasted all his time and too much of mine.
On the first day back he asked me to repeat out loud in the changing room what he had written, which I did: cue nervous laughter from the other boys who probably knew that he had no business doing that.
Then he asked me what my parents had said.
My Dad said you're right, Sir, games and PE are a waste of the time of intelligent pupils and half-intelligent teachers, and you should stick to History and English, he'd heard you were adequate at those.
Cue laughter that was not at all nervous and entirely at his expense, and he had to pretend to join in, because he knew, and I knew he knew, that that was exactly what my father had said.
And a few years later when I was studying for the law and learnt the first rule of cross-examination which is Never ask a question to which you do not know the truthful answer I remembered the poor silly chap trying to be an amateur cross-examiner and coming unstuck!