I think shouting fire in a crowded theatre is fine if there is a fire in the theatre.
Also, if everyone in the theatre has gathered to witness an execution by firing squad, they are probably expecting someone to shout fire.
I even feel it is fine to shout fire in a crowded theatre and start a panic if the people in the theatre are attending a Dictators for Starvation conference or a Hitlers Anonymous meeting.
Other than that, shouting fire in a crowded theatre is wrong and I should probably stop doing it.
Shouting fire in a crowded theatre . . . eh.