Used to work part time at a cinema to make some money whilst I did my degree at uni. During each shift you had to go into all the screens (an average of 3 times throughout each showing of a film) to check nobody was trying to record the movie.
One shift it was my turn to go in to the screens and and this was when the remake of the Evil Dead had just come out. I walked in to a screen and down the side aisle to look up at the seating (looking for camera lights, people sitting weirldy to hide cameras etc) but it was a really tense, quiet, dark part of the film and as my uniform was all black I guess I blended in a little oo well. I was stood by a shoulder high parition wall looking up at the people when suddenly the screen lit up with a jumpy part of the film and I realised too late I was stood right next to a woman sat watching the film.
Well, the scary part of the film combined with my suddenly appearing next to this poor woman meant she literally fucking screamed out loud. Her popcorn went flying, her drink went sideways, her hands flew up - she fucking screamed a scream of pure terror at this random person in black looming next to her as some fucked up shit happened on screen.
Well, I lost it.
I tried to quietly apologise but I was in absolute hysterics. A few people had obviously seen what happened and were laughing too but my eyes were watering and I was shaking with laughing. I had to sprint out the screen so I didn't disturb the movie anymore than I already had done. My manager found me crying and doubled over with laughter and when I told him what happened he started pissing himself as well.
I was so hysterical he let me have my break early just to get me off the customer floor. I periodically think back to that and still laugh myself silly, that poor woman.