Mockumentaries, e.g. Spinal Tap. It seems like everybody loves these movies yet they give me migraines. The brain pain these movies cause me is so strong, I hesitate to even bring them up. Even thinking of them makes me wince. I didn't know "painfully unfunny" was a literal sensation until I saw Best in Show, and all subsequent mockumenaries I've seen have been just as bad if not worse. I now refuse to watch another for the rest of my life.