Ok, you and the wife are at the theatres. You are texting the babysitter who is posing as your three year old daughter. You do this, in a rare moment of 'I never do this during the previews but my three year old is being very funny', during the previews.
An older gentlemen behind you tells you to turn the cellphone off. You note he is angry.
At what point do you think to yourself, "I can take this old geriatric in my sleep", and tell him to frak off?
Geriatric goes to find a manager. He comes back managerless.
At what point do you think to yourself, "I'm going to take this old geriatric outside," and ask grandpa if he told tales to management on you?
At what point do you throw your bag of popcorn at him?
Me, I think you'd probably tell the geriatric you were sorry, it is your three year old daughter, possibly make like you were worried about her, and put the phone away.
This doesn't excuse the geriatric bringing a gun to a theatre and shooting someone to death, I just think you'd behave better than the dead gentleman did.