I find the best way to handle a situation where a dumbass is talking on a phone in a theater is to be insufferably polite.
"Excuse me, sir/ma'am, I hate to interrupt, but you are disturbing those of us around you. I would appreciate it very much if you could be quiet. That would be very kind of you. Thanks."
I usually get slack-jawed responses to that approach. ...and wonderful silence. How do you reply with any sort of animosity to someone who is nice to you?
If you go in with guns blazing, people get their backs up. Obviously, the situation with the meat thermometer got out of hand whereas a little politeness could have defused the situation.
If all else fails, go get the manager. It's their theater's reputation on the line & they're always happy to help out with taking idiots.
I remember going to see "Apocalypto" a few years back & some moron was droning on endlessly.... I just avoided any confrontation & got an usher. He approached the jerk, who immediately turned around & said I was disturbing
him. Well, the usher didn't buy it, telling the clown to stop swearing at him: It was really quite funny.
Then patron went on to say, "we're not making any fucking noise!" ...right then, his cell phone started ringing. He was told to be quiet or leave. He shut up.