Related to the other thread about filming without a permit... I think I've told this around here before, but this is one of maybe three times in my life that I've seriously felt "near death" and the only filmmaking-related one.
I was shooting my first 'film', a 45-minute epic Lord of the Flies-inspired western called "Trouble at the Circle-K" for a high-school history class. I was also one of the lead actors. We had a flashback which showed how my character ended up at Thaddeus Yount's School For Rejects due to his involvement in a sperm-bank robbery. We decided to film this outside a real bank.
The scene: A beat-up old car pulls up in front of the bank with two people in it - I'm driving, and 'Jimmy' - a notorious kleptomaniac - is in the passenger seat. Jimmy says "I'll be back in a second - I need to make a withdrawal for my sister" and jumps out of the car. Seconds later the engine stalls, and I panic trying to restart it. Jimmy jumps into the car carrying a clear bottle half-full of white liquid and shouts "lets go!!!!!" but the car still wont start. Suddenly a police officer steps up to the passenger window with a gun and yells "Police - hands up!". FADE TO BLACK.
So we went to a local bank, and I went in and told them what we were doing. They actually had no problem with it, so we ran through the scene out front a few times, got a good take, and moved on with the rest of the project.
About a week later I was going through all the footage we'd shot so far and couldn't find that scene anywhere. I finally realized that somehow we'd managed to accidentally tape over it while shooting a different scene. Nothing we could do but shoot it again - so we went back to the same bank.
This time it was a Sunday though, and the bank was closed, so we couldn't let anyone there know what was going on. We figured since no one was there to complain though we'd be fine.
So we shoot the scene once more. Unfortunately our actor playing the police officer had left his security guard jacket at home, so all he had was a dark blue windbreaker. We thought it looked close enough to work as a police officer - although in retrospect the combination of the windbreaker, his slicked back hair, jeans and wayfarers did kind of make him look like any generic member of one of the local gangs.
As the scene ends, and our 'officer' steps up to the car with his gun (a pink squirt gun I'd spray-painted black) there was a screeching of tires as an old white car driving through the parking lot slammed on his brakes. The driver leapt out, leveled a gun at our actor across the top of the car, and yelled "police, freeze! Drop the gun!". Our actor half turned to see this, said "Oh, ok." and dropped the gun... straight through the driver's side window of the car and into my lap.
I glanced down at the gun in my lap, glanced back up and two police officers lean around the corner of the building in front of me - one with a pistol, and the other with a shotgun, both pointed straight at me. Suddenly four patrol cars speed around the corner to surround our car and we quickly have more than a dozen guns aimed at us and one very excited K9 straining at his leash to charge us. So the passenger and I raise our hands out the front windows as high as we can.
Now, we were shooting this whole scene from the back seat of the car. This meant there were no visible cameras outside of the car, which certainly didn't lend credence to our panicked shouts of "We're filming a movie!". It also meant our cameraman, who was focused on the camera viewfinder, had absolutely no idea what was going on outside of the car. So he hits the fade button (we had no access to real editing equipment at the time, so we were doing a lot in camera) and the shot fades to black as this all happens around us. He puts the camera down and is asking us what's going on, we're yelling at him to just get his hands up.
One by one they have us get out and back away from the car at gunpoint. We're handcuffed and thrown in the back of their cruisers. They're asking us what we claim, and we're replying with things like "Honors English & History!". One of my friends asks them "Is this going on our permanent record?" and "Will I still be able to get into college?!?". They finally clear the car, the K9 officer sends the dog in to check that no one is hiding, and as he gets the dog out of the car he picks up the gun from the car and yells "Hey guys, it really is a toy gun!". After that things got a little less tense.
It turned out someone had called the police from a bar across the street when they saw us with a gun. There'd been half a dozen armed hold-ups in the past month at the ATM of the bank we were at, so the police had every reason to believe they were actually witnessing a crime taking place.
In the end they took off the handcuffs, sat us all down on the curb, and we got an angry lecture about why hollywood films in studios instead of on the street. They called our school and we got another lecture in class the next day from our teacher. To this day, over 20 years later, the actor playing "Jimmy" still hasn't told his parents about it. It didn't end up on our permanent records, we all still got into college - and I think we even got an "A" on the project.
And that project, probably more than any other single thing I can think of, changed the entire trajectory of my life - it was what made me realize I wanted to be a filmmaker. But one wrong move on our part, or one cop who'd had a little to much coffee that morning, and it could have easily changed my life in a far less positive way.