So there I was, 12th grade of high school (roughly late 1982), sitting in Trigonometry class and day-dreaming as I stared out the window, hoping for snow. The teacher, Mr. Slivoskey, asked one young, female, Asian student to solve a problem on the board, and of course, show all her work. She started working furiously on the left side of the board, and proceeded to fill the entire board, mapping out a hugely complex equation that no sane human being would ever use in real life. Her breakdown of the equation literally *FILLED* the board from end to end and as she was writing it out, I was mentally checking her work; as was the teacher (and probably the rest of the class too). Half way through, she missed a negative symbol, and my heart sank for her because I knew there would be hell to pay.
When she was finished, she stepped back to allow the teacher access to the board. He started at the upper left corner and weaved his way through her calculations. When he got to the missing negative symbol, he stopped and pointedly mentioned “Because you missed this, your final answer should be a negative number; not a positive number”.
From 1/2 way back of the room comes my voice in the most sarcastic tone one could imagine: “Mer-ry Christ-mess!“. Mr Slivoskey turned and stared directly at me, but my job was done, and he knew it. 😉