I believe I've met you at one of the DC Chapter dinners after maybe GOE. If that was you, you seem like a nice person. I really doubt that even throwing their drinks on you would have made you kill them, or try to use it as a defense in court.
I understand being reminded of a past outrage in a theater, and how annoying the media generation has become. I sat through a recent concert in a front row seat with the person next to me viewing the entire concert on the iPad in his lap instead of what was in front of his eyes, had he raised them to the stage. But I don't understand using that annoyance it as a rationale for killing someone.
I think Jesus' command to, "Turn the other cheek" is relevant here.
A slap on the cheek is not a potentially deadly assault. It's an insult, much like having a drink or popcorn thrown on you.
Being insulted, as such, does not justify violence in return, much less lethal force.
Violence and deadly force are sometimes justified, but not because someone has dissed you.