But her professor refused to do so, and leave all the things to TA. The prof said the TA’s marking is final. Therefore, my friend she got a bit mad, and she kept emailing the prof regarding this issue. However, she did not wrote the email in a polite way. The prof got really angry about her email. Then the prof said he reviewed her paper and deducted her bonus question mark. After that, my friend did not response, and she just want to drop the course. The next day, the prof kept pushing this matter, he said he wants to meet my friend because he thinks my friend cheated on the exam. He said my friend did not show all the work of the last two questions( btw: the instruction did not ask students to show all the answers). In the meeting, the prof threatened my friend that he will hand in a form indicating my friend cheated unless she drops the course.Therefore, I think he is completely being unreasonable and immature. I can understand why he got mad, because the email was not written in a polite way. However, I don't think he can just accuse anyone that piss him off.Thus, I want to ask you guys how my friend or everyone can protect themselves, and if possible, how to sue the professor for unreasonably accuse student cheating.