Just remember why you are there— to learn the course material. Try not to focus on C. Since you’ve known him for a long time, just try to let it go and be friendly. I’ve seen those kinds of people that C is, over-bearing, and your feelings are completely understandable.

I agree that you didn’t need to get into it with C about the dates of the course, as that was the professor’s job, and he was telling C the way is was going to be (which was to your liking). You set yourself up for friction by treading where you didn’t need to.