I don't recommend this, but I still want to share this story. A few years ago I was with riding POTC in Anaheim with a large group of fellow Disney fans from another forum. The people in the boat directly behind us, not part of our group, kept taking flash pictures. I don't mean that they took a few pictures, I mean it was constant. It wasn't just one person, it was most of the people in the boat. It was so bad that one of the CM's repeatedly used the PA to politely ask them to stop. They ignored the repeated requests.
Towards the end of the ride some of the passengers in my boat asked me if I would use my flash to make a point. I had a Nikon SB800, which is a pretty heavy-duty flash. It has a test mode where you can press a button and it will discharge at full strength. I thought about the request and I didn't want to do it at first, but, since the people behind me wouldn't stop using their flashes, I changed my mind. I turned it on, waited for it to power up, aimed it behind me, and pressed the button. The flash was quite bright, and the people behind us got the point because there were no flashes for the rest of the ride.
Again, I don't recommend this, and I'm not proud of it. I just think the story is worth telling. Sometimes you have to fight fire with fire when nothing else works, and this did work. It worked really well.