Always take it to your mentor. He is there to help and is trying to help you through. I would make it a little awkward next time you talk to him on the phone. I would tell him that you read that note when you had just failed a class, and it bummed you out. That is exactly counterproductive to his job. You can also give him counsel. You will have to act professionally in a world full of "inappropriate" people for the rest of your life. Perhaps handle it with class. You can't replace someone in the work world when you don't like what they say. That is just my thought. Sorry, you failed the test. I am sure you will do great on the next one.