It's been said a lot but I can't stand awkward based humor, particularly when the likeable character digs themselves a hole. When I was a kid I couldn't watch Everybody Loves Raymond, I had to leave the room because I just couldn't stand watching it. Even now when anything awkward happens on TV I find myself just staring at my feet or at the wall.
Also, not TV/movie but the mission in Far Cry 3 in which you have to kill the cheetahs with the flamethrower. I'm usually fine with violence, especially in video games but something about the way the cheetahs acted when on fire just made me hate myself. Couldn't touch video games for a couple of weeks after that.