8. The Clocker. Most people switch cell phone ringers to vibrate, but there is a new breed, and he doesn't wear a watch. Instead, he checks his cell phone clock every 30 minutes, lighting up the theater like a Christmas tree. Cover the LCD and be discreet.
Yes, we can see it, even if it's only on for a second. You committed to two hours (83 minutes if it is a SNL movie), deal with it. If you can't recognize when the third act starts and do the appropriate math, buy a watch.
I have found it helpful to do the stretching exercises my physical therapist recommends. Do some core strengthening exercises, such as the ones highlighted at The Mayo Clinic. By keeping your core strong, your back won't put itself in a position to cause that sciatica pain you are having.