If there really is a fire in a crowded theater shouting “Fire!” probably isn’t indicated. What is one supposed to do?
Pull the fire alarm?
Or, yell fire. Since no one actually does that, I think it would be pretty effective.
nm
Walk to the nearest door, then yell fire.
Walk to the nearest exist and shout, “Walk to the nearest exit.” If no one responds shout, “Get out of here! There’s a fire in the theater!”
The phrase “Yelling ‘Fire’ in a crowded theatre” is used to describe situations where there is no danger and a person deliberately causes a panic. It’s from a Supreme Court decision where it’s used as an example of legally restrictable speech. If there’s actually a fire, you’d probably want to let everyone know, though yelling “Fire!” isn’t exactly right; you’d do better to stand up and announce “Everyone proceed to the rear exits-- there’s a fire backstage.” Unless the fire’s in the lobby, when you’d indicate other exits, or whatever.
May I have your attention, May I have your attention. There has been an emergency reported in the building. Please go to the nearest exit and exit the building. Please use the satirs, do not use the elevators.
This is no time for sex! The building is on fire!
Maybe that’s why it’s on fire. Oh baby.
You forgot: “This is not a drill. I repeat, this is not a drill.”
It is if they’re using the satirs. 
If there is a fire in a crowded theater, anyone not using their cell phone will recognize the danger. Get up quietly and walk out.
Outstanding!
Grinning like this :D, I applaud you.