I never want to be overly involved in the business of others, but there have been situations where I felt obligated to intervene - at pay to shoot ranges and common "national forest ranges".
Honestly the worst things I've seen were this old man trying to "clean up downrange" while there are over a dozen other people shooting... I called a cease fire (it works even in a pseudo range in the middle of the forest) and ran over to him. I told him it was unsafe for him to be there and that the other folks here would appreciate it if he would limit his time down range to target setup. He got a bit uppidy and grumbled something about "if it doesn't get cleaned up theyll shut this place down". I responded to him with "if you get shot or hit by a ricochet it will DEFINITELY get shut down". He grumbled and went off, but I couldnt believe the nerve of that guy to just walk down range and start picking up trash while people are firing... What kind of logic is that? A couple pieces of cardboard targets aren't worth your life crazy man!!
The only other time was out at a proper range with a rangemaster and all that. This young man I guess you could say and his lady friend were out and to our left at the outdoor range. He kept his finger on the trigger even when he wasn't firing/while he was talking which really urks me. The worst part though was his lady friend - not saying ladies can't use firearms I'm just telling a true story - would fire then start laughing and look back at her man friend with her finger on the trigger and the muzzle almost pointing straight down the firing line at us. Ahhhh..... It's best to, without being rude if possible, educate people on what safety concepts they are not following and that it would make you feel safer if they would.
4 Weapon Safety Rules (and the hidden 5th rule..):
Treat every weapon as if it was loaded
Never point a weapon at anything you do not intend to shoot
Keep your finger straight and off the trigger until you are ready to fire
Keep your weapon on safe (when applicable) until you intend to fire
(extra) Know your target and what lies beyond
Follow these rules and practice good and constant muzzle awareness (muzzle never points at or crosses a person) and you should be set. It's not rocket science, but people still screw it up...