I will never ever send this letter, but I need to write it.

Dear Paul,
This letter is in reference to your behavior to me yesterday morning. I doubt you know this, but I have not studied your subject before, and was studying all of Wednesday and part of Thursday before the test.
Therefore, it was a shock to receive my paper from a month ago, and be told that I had mis-done the assignment. "I still gave you a .... grade," you said, "but follow the instructions next time."
I am not debating my grade (80%) or the fact that I should have made my intent clearer closer to the due date. (You don't seem to remember me checking the aspect of the assignment you had such issue with at the middle of the semester, but I assure you that it happened.)
Paul, I am debating how you went about it. First of all, your comments on the paper may have been written with good intentions, but they were actually very harsh. "How could you think this was okay to do when the paper was worth 20% of your grade?" may have been meant inquisitively, but it came off as accusatory. Also, I find fault with your timing. If you were so incensed with me, I would have preferred for you to take this up with me after the final examination had been completed. Paul, your remarks (written and spoken) made me cry. It took extraordinary strength of character to fall back into "finals mode" and try and do the best I could. It was also very painful to try to not think about your comments as I was doing the test itself.
Last, but certainly not least, I believe your conduct during the exam itself was unprofessional. As the room was quiet and we were writing, you made three loud announcements and questioned the class as a whole. "Do you know Person #1, Person #2, or Person #3's cell phone numbers?? Please text them! They're missing the final!" A few minutes went by, then: "Does anyone have a laptop or tablet with them? .... Can you fire it up? I need to find your classmates." Paul, this last one was my favorite. A student walked in at 10:45 when the final began at 10:30. You exclaimed, "Talk to me! You're fifteen minutes late!! What is your excuse?"
Paul, all of this behavior was disruptive and unprofessional of you. You may know the material, and I am certainly glad that you have faith that we do as well, but this was not a typical class period. This was the final exam. Finals week is a very stressful time in the life of a college student. We do not need emotional upheaval or disruptions during the test itself.
This had made me to never take a class with you again. This will be my first and my last class with you.
Take care.
Signed,
Me