As you go through life you are going to be in all kinds of all situations with all kinds of people. You are going to have to decide how important this person is to your future, and what you truly believe and want to stand for!

My youngest son has a bachelor of science degree in human biology, a tech degree in radiology and now teaching degree.

In his junior year of college he got a D in ethics, because he did not agree with his professor about ethics. She was married, pregnant with the child of another professor who was also married, and she thought it was ok. He flat out told her she had no business teaching him ethics. She could not flunk him because he passed all the tests, but she did keep him off the honor roll. Stand off. He is successful and happy, she's a divorced single mom.

Pick your battles! Some are worth it, some are not.

I think everyone's advice is good so far. It's tough, because with professors you don't just want their approval emotionally, you need it for a grade!

There is always one professor every semester I HATE, but I need A's for my major. I wrote down a list of what I do and I tape it inside my binder.

1. Show up, sit in the front row and look interested!
2. Turn in every assignment on time. This gives you so much credibility with professors for the times you do screw up unavoidably.
3. Ask questions! Professors LOVE the subjects they teach, they dedicate their lives to it. Ask intelligent questions about the class topics (after class or before if they seem too off-topic or individual). It is a lot harder to fail someone who has taken a personal interest in you.
4. Keep in email contact with the professor once every couple weeks. This is counter-intuitive because after class, you don't want to even think about it for another week, but this works for the same reason that 1 and 3 do -- it's harder to kill the puppy you name.

Last semester I was really unhappy in my statistics and probability class, but I did all these things and then got a reference letter from the professor that said that I was the best student in the class. His evaluation was not as glowing, but that was anonymous