I am very seriously religious, but never mention it to others because I notice it makes them uncomfortable. Plus, I don't want anyone to feel that I am telling them my beliefs are more right than theirs and hurt their feelings. If I feel someone else is overstepping their boundaries, I usually either joke to change the subject or ask them a question about why they feel that way, so they realize I'm a little bugged and (hopefully) drop it.
However, two times in the past few years, I have had professors step over the line in the middle of class. The first time, I had a professor who had told the class several times that she converted from my faith because she thought its tenets were wrong and she felt it too oppressive. On this particular day she told the class a "fact" about what my faith holds which I knew to be wrong. I raised my hand and mentioned that I was "pretty sure that xx's do believe yy". The teacher asked me how I knew, and I said I learned about it in a class (true, just very vague about circumstances). She then said that she knew I was wrong, and several other students chimed in to support her position. During the rest of class, she kept harping on this idea and mentioning how she had converted because of "wrong" ideas such as this one. I started to feel really bothered about the negative way she was portraying my religion, but I never said anything to her.
The second time, a different professor had been similarly clear about how she disliked my faith, except she cited the fact that people of my religion had often oppressed her/tried to convert her/mocked her ideas/etc. She generalized this to the idea that people of my faith tended to impose their ideals on people of hers, rather than just her. Her most popular examples were where coworkers "insulted" her and she mentioned the fact to a supervisor. (Tangentially-related: She was also very political and often encouraged students to go to rallies in support of her chosen political candidate or position. Other students would sometimes mention before she came in the room that they felt unable to share their ideas politically because she might dock their grade for being "wrong" or insulting to her.) Again, I stayed silent but was seriously bugged. There was never a specific time when she said something objectively wrong, so I never felt justified in speaking up.
I was so bothered at one point that I went to a support group for my faith on campus. They actually mentioned (without anyone bringing it up) that they intended to have discussions throughout the year about the anti-xx sentiments on campus. The group leader mentioned how uncomfortable moments could be great opportunities to reexamine and strengthen one's own faith. Not surprisingly, they did not come up with a miracle cure-all for the discomfort part at that single meeting.
My question: If this happens in the future, how do I ask someone in a position of authority to stop talking about my religion? I don't want to tell them my religion (I feel like it will lower me in their estimation, or put my objectivity into question) or convince them to change their ideas. I also don't want to seem aggressive and get reported to a conduct board. However, I don't want to fight back tears and I just can't seem to toughen up to the point where I can calmly do nothing. Is there any action I can take to make class (or another situation) more bearable?