The worst film I've ever seen was also the only one that's ever caused me physical pain. It was called
wavelength, and I watched it as part of a film class. The entire film is a 45 minute zoom across a room. While this is happening, a tone plays in the background, starting at 100Hz, and slowly increasing to 10kHz. My head hurt something special by the end. I told the professor after class that if you took me to Guantanamo and made me watch that a few times, I'd tell him whatever he wanted to hear.