Stupidity: When Flint Marko is escaping from the police, he climbs a chain link fence into a test facility. Besides having a chain link fence, there should have also been security cameras around the area as well as guards to prevent anyone from trying to get in. Plus, when the scientist notice on their computers that there's an increase in mass, one of them simply assumes it's a bird and then they continue their experiment. Instead of making assumptions, they should have halted their experiment and have someone take a look to see what caused the increase of mass.
Stupidity: A load of cars is in the tunnel with the overhead lights off, and none of them has thought to put their own lights on (as covered already). Then John gets out of the car, only for one car to suddenly flick its lights on and nearly run him over, having been driving at full speed in the total darkness, apparently.
Stupidity: When Stuntman Mike is taking photos of the girls, he is shooting with the lens cap on the camera.