When I was teaching my younger cousin (then age 12) to shoot...
...he, being a good kid but also an incorrigible wisea$$ (after all, he was 12), asked me what I'd do if he "accidentally" swept me with the muzzle at the range. He asked this in front of his grandmother, who is a former Army medic.
I told him I'd punch him in the head, and the day at the range would end rather abruptly.
He looked at me, with that 12 year old, you-can't-be-serious-but-I'm-not-quite-sure half-smile, and asked, "you're kidding, right?"
Before I could answer, his grandmother said "no, he's serious. And if he didn't punch you in the head, I would."
We then went to the range for the first of several, uneventful sessions.
But frankly, I would have punched him in the head if merited. I wouldn't have hurt him too badly, but I'd have done whatever necessary to get his full attention.
Not only did he not ever sweep me (or anybody else) with a muzzle, but he got a lot of compliments on his safe weapons handling from the rangers who instructed his hunter's safety course a few weeks later. On top of that, he was the only kid to hit all of his targets. Top score in the classroom and at the range for his age group.
To this day, he's quick to point out to me any safety violations he sees, and he is very aware of his muzzle.
He pays attention to where his gun is pointing, too.