At my club, every member is mandated to act as a Range Officer, and stop someone from doing anything un-safe. If the Range officer is distracted, or brain dead, Yell at the guy. And Yell first at the guy who is endangering someone who is down working on targets. Occasionally all of us have been absent minded and stepped up to do something with the gun before the range is clear. I appreciate someone yelling at me about that. I can't imagine a shooter NOT appreciating a warning that he is doing something unsafe.
So, be a friend, a good friend to everyone on the range. But must of all, be a friend to the owners of the range. It will be they who are sued, and the range might be closed because someone who could have said something to an idiot, didn't.
I was on a public range when I was a young teen, when a guy a few benches down from us was waiving his gun around every time he fire off-hand. He would turn to ask his buddy where he hit, and the muzzle of the gun would sweep the firing line first to the left, and then to the right when he swung back. Our range officer had been called away to another range to help repair something, and the first time I was aware of this idiot was when I saw other shooters all up and down the line getting up and walking back out of his line of " muzzle ". Finally, a small, but very angry group of men walked over, and someone told this guy what he was doing wrong, and told both of them if they did it again, they would be lucky of all that happened to them was being thrown off the range! They got the message. I learned an invaluable lesson.