While I agree that the first two are more "bad etiquette" than screaming red-flag safety violations, they do bespeak a lack of attention on the part of the guy holding the broken-open gun. Absent-mindedness in one situation means he's more likely to be absent-minded in others. As taught in the courses "always keep the muzzle pointed in a safe direction".
A quiet word to the guy in situation #1 "hey - I was behind you and, while I could see the gun was broken open, it still made me uncomfortable to have the muzzles pointed in my general direction." If they guy gets on his high horse, I find someone new to shoot with.
Situation #2 seems to be one of the most common safety problems with shotgun sports. People muzzle others, and get muzzled, all the time. I don't like it one bit. Again, absent-mindedness. A quiet word done in the spirit of "praise in public, chew out in private" and see what the reaction is.
Situation #3 is one where someone calling an immediate cease-fire would be well within bounds. The shooter evidently had his concentration on remedying his problem and needed someone shouting to break in on his attention and move it to where his muzzle was pointing.
I'd be reluctant to squad with him.
Situation #4 is tougher. My club has a member who was a PBY pilot and would sometimes wear his "Ford Island" hat (i.e. 12/7/41) while shooting. And he only gave up shooting spring of last year - new girlfriend. He was also the most safe guy there. Not all older guys are so mindful or safe. It's hard to have to have a safety officer alongside all shooters - both from manpower concerns and also out of fear of insulting the shooter. So, checking with the shooter along the lines of blaming the gun - even though he probably knew it was his finger - might be enough. But I'd be watching him like a hawk to see if trigger-finger control was an on-going problem. If it was, I'd move on.
At my club, our watchword is that one accident is enough to close us down, so everyone needs to be extra-safe at all times. So far it's worked.
