Having a flashlight--good idea. Trying to use it to blind a guy with a rifle--maybe not such a great idea.
I always carry a flashlight; I don't know how folks get along without them. Mine's over 100 lumens--bright enough to leave a large blind spot in your vision for awhile, especially if you're dark-adapted and the light is shined from up close. From across a theater, I doubt it would do anything but make the guy angry and provide a good aiming point.