Crappy projectors - I saw Sisters recently and the right half of the screen was noticeably dimmer than the left, to the point that it sometimes became difficult to discern finer details. It sucked.

Unlikeable characters, especially the main character. I don't dislike many movies, but I couldn't stand "Tammy" - Melissa McCarthy's character had zero redeeming qualities for me and the whole movie just made me feel ill.