In the above video, you see a seemingly normal man shooting at the range, with his instructor standing behind him.
He then hesitates in shooting, turns the gun around, and fires a round into his own chest. The bullet travels straight through him and into the instructor standing behind him.
The instructor falls to the ground and attempts to move away from any addition fire, as the man just stands there. He eventually walks over to a chair and slumps down.
Always keep your guard up. Even in the most seemingly safe places, such as a shooting range, there can still be a crazy person with no regard for human life.