I am currently a student in computer science. Because of my specialization, there are only two groups I could choose for writing my thesis. I spoke with both and then chose one.
But now, my current professor is very hard, unfair and personally attacking me when giving feedback. This is a known issue with him amongst the other students but until my last oral test (which was not good), I never encountered problems with him.
I want to speak with the other professor and ask whether I can write my thesis in his group. I wonder what I should answer if he asks why I changed my mind. I would answer that my professor is becoming enormously rude. But I do not feel that this is the professional answer. How can I prepare for this second talk?