Crimes of hyperbole?

Why if you yell "Fire!" in a movie theatre is it a crime?

Spartanburg County, South Carolina - A 78-year-old vet was arrested and charged with making threats against the President after saying he’d like to kill the United States President, Barack Obama.

A shock jock and blogger was found guilty of threatening to kill three federal judges in Chicago, Illinois; it appears from the report he did not say he wanted to kill them, but that he believed they deserved to be killed.

What is hyperbole? When is hyperbole considered a crime? Is the suggestion of killing the U.S. President different than saying you will or want to kill the U.S. President? When is free speech not free? When is a U.S. Citizen's right to free speech curtailed in favor of expediency?