Was there ever a case involving someone who yelled fire in a crowded theater?
The reason why one would find that act heinous is because early theatres were often set on fire, with flammable celluloid running past a bright hot light bulb, and a correct warning of fire would have to be acted on quickly. A false alarm of fire would lead to many lives risked, at least, and perhaps lost.
It was the frequency of bad fires that made it subject to the analogy, which has now outlived the hazard.
I once shouted “Movie Theater” during a fire. Nobody seemed to notice.
http://en.wikipedia.org/wiki/Schenck_v._United_States
In the opinion's most famous passage, Justice Holmes sets out the "clear and present danger" test: "The question in every case is whether the words used are used in such circumstances and are of such a nature as to create a clear and present danger that they will bring about the substantive evils that Congress has a right to prevent." This case is also the source of the phrase "shouting fire in a crowded theater", paraphrased from Holmes' assertion that "the most stringent protection of free speech would not protect a man in falsely shouting fire in a theatre and causing a panic."