The only film I've ever walked out on was one for one of my film classes - David Lynch's "Lost Highway." I believe I screamed "This is (expletive)!" and left. I enjoy a lot of his films, but that was a colossal mess and had no business in a university film class.
Man, I hated film classes. I took a couple at UNI and couldn't believe the pretentious drivel I was forced to sit through. At one point, if I had seen another French film, I was going to rip the videocassette apart. Still can barely sit through 'Amelie'. I do just because Audrey Tautou is in the flick.