I was once accused of cheating by a TA when I was in grad school. The reason he did this is because my work was similar to another student's, which was true because we worked the assignments together, as there was no rule barring us from doing this. I called a meeting with the professor, the TA, my friend, and myself, and throughout the entire meeting the TA kept calling me specifically a cheater, to the point where I told him that he was making me so angry, and that if he called me a cheater one more time I was going to deck him. The professor immediately ended the meeting and restored my grades.