There are a lot of little cues here that suggest, to me, that this was a man who felt like he had authority over others and lost his temper when he felt like that authority was being challenged.
Obviously, this texting incident was not about caring deeply about the other movie-goers experiences. Getting into even the sort of verbal tussle he did - much less shooting someone dead - is far more distracting than the little light on a cellphone screen.
Go back a little farther, and there's that other incident where he fussed at someone for texting in a theater... after which, he continued to assert his authority over them, appointing himself as some sort of watchdog of their behavior. Following someone on their way to the bathroom is creepy as hell, not to mention unnecessarily threatening. Why would he do that? If I were writing his character, I would think it was because he felt righteous and powerful when he asserted his authority over her, and consciously or (more likely) not, he wanted to continue feeling that way.
You can go all the way back to his daughter's testimony, talking about how strict and firm he was with her, but how he was always ready to take over when she needed something.
You can look at the career path he chose.
The man liked his authority.
Also, I'm reminded of two of my grandfathers, both of whom enjoyed considerable authority throughout their lives, but began to lose it as they aged. Others had to take more care of them, causing them to lose some autonomy, and they began to lose abilities they had once prided themselves on. In both cases, they became much more assertive and began to jealously guard what authority they had left, to the point of doing and saying things they wouldn't have dreamed of a few years before.
I know that security guards catch a lot of flak. They aren't seen as "real" police. They are often under qualified and usually not respected even by the teenagers they shoo away. To go from being an officer - especially a high ranking one - to being a security guard has to feel like a tremendous loss of respect. To lose the ability to do things you once enjoyed, and to lose your edge on top of it all probably felt like salt in a wound.
But it's easy to feel like a big man when you have a loaded gun in your lap.
And this was a man who knew the law. He may have immediately verbally identified the thrown object as a harmless bag of popcorn, ("I'll teach you to...") but what he told authorities was that he was "assaulted with an unknown object." In fact, immediately after the event, a witness (Hamilton) testified that the shooter told him, quote:
'I just got hit by something and look at my eye'.
But Hamilton says he didn't see any injury on Reeves' face.
"Something." Not popcorn. And he wanted to claim an injury.
To me, this reeks of someone who wanted to assert authority over others, not some harmless, confused old man who just got scared and caught up in the moment.
