I had an advanced math exam (in physics) and I was at my second page for exercise 1 when the prof wandered around the class. He stopped at me, read a bit, sighted and then said loudly "ladies and gentlemen, I just would like to point out that if your handwriting is not too big, the solution to exercise 1 could fit on one line, max two. Thank you."
What a way to fuck up my day :)