I've had two.
The first one was went I went to see Lord of the Ring at a dollar theater in a mall. First, the screen was tiny. I have literally seen TVs that were bigger than their screen. Granted, those TVs were big TVs but still... The seats were horrible. They were wood and flat and just plain wrong. Plus, there was some idiot right behind me who wouldn't shut up. Every single time Hobbit feet were on the screen, the guy would laugh and go, "Look and them feet! Them are some huge feet! Hairy too!"
Fortunately, it was my fourth or fifth time to see the mobie so...
*shrugs*
The next bad experience was when I went to see Star Wars: Episode II for the second time. When Padme and Anakin were starting to land on Geonosis, the sound started to crack and pop and the characters started to sound like robots when they talked. I got a free movie ticket.
*shrugs and walks away*