"shouting fire in a crowded theater"

     [This is a fast-access FAQ excerpt.]
This is from the U.S. Supreme Court's decision in Schenck v. U.S.
(1919), setting limits on the freedom of speech guaranteed by the
First Amendment to the Constitution.  Justice Oliver Wendell Holmes,
Junior, wrote:  "The most stringent protection of free speech would
not protect a man falsely shouting fire in a theater and causing a
panic."