I had a friend who was, shall we say, cerebrally challenged. He wanted to learn to shoot a pistol. This was about 20 years ago, and we lived in Greenwood, so I took him to Don's Guns. I had a S&W Model 19, .357. I showed him how to aim, breath, and gently squeeze the trigger, in the single action mode. Now, I want you to realize that the pistol was verrrry light on the trigger when the hammer was cocked.
He aims the revolver down range, cocks the hammer, and starts to squeeze. At this point he turns to me, the barrel about two feet from my chest, and says "But what if...." Fighting to remain calm, I quietly told him to lay the gun down. He just looked at me puzzled, hammer cocked, finger on the trigger, aimed dead at my chest from two feet away. Once again I quietly told him to lay the gun down, and step back. Once he did this I had him up against the wall, yelling at him to never point a gun at me again. The lesson was over.
I have taught several people to shoot since then, but I always start and finish the lesson or demonstration with the admonishment not to point a gun at something your not ready to destroy. What should be common sense, can be extremely uncommon. Not telling a noob to not point a gun at you is very dumb. It gets expensive if you have to buy a new pair of shorts after every lesson.
Wow, what a story. I do the same thing about providing instructions beforehand as well. I also stand behind the shooter, offset a little. It helps with observations and the ability to deflect them back down range by pushing on one of their shoulders (preventing them from turning).