I can fairly safely presume that you have, at some point, used the phrase 'fire in a crowded theater', or at least heard of it. I have too. (If for some reason you haven't, you'll pick it up soon enough. Just keep plowing on.) You may or may not also be aware that the phrase originated from an old Supreme Court case of some sort.
Okay. Which case?
I ask because you might not want to use it again once you hear that, well, first, the quoting is wrong. Trevor Timm of the Atlantic has a much better writeup on this than I do, but I'll give you the 99-cent version.
Anyway. The correct quote is, "The most stringent protection of free speech would not protect a man in falsely shouting fire in a theatre and
causing a panic." Second, and more importantly, the case in question was Schenck v. United States back in 1919. The ruling was 9-0; the quote was given by Oliver Wendell Holmes. Schenck was Charles Schenck, of the Socialist Party. This was the era of World War 1, and the draft was active. What got Schenck hauled into court was that he printed and distributed pamphlets to potential draftees urging them to "assert their rights" and to petition for the draft's repeal. That's it. For that, Schenck was found in violation of the Espionage Act of 1917, which made it illegal to interfere with military operations or military recruitment, or to promote insubordination. In the Court's ruling, which upheld the Espionage Act, Schenck's mild little flower-power pamphlet qualified as a "clear and present danger" to military recruitment. Schenck wound up spending six months in prison.
Holmes realized pretty quickly that he screwed up. It was too late for Schenck, but it wasn't long- the same Court term, in fact- before he flipped and started ruling in favor of dissenters in similar cases. (The dissenters would still lose a whole bunch, though, because there were still eight other justices who hadn't come to the same conclusion.) In Abrams v. United States, argued later in 1919, Holmes was now saying, "The ultimate good desired is better reached by free trade in ideas --
that the best test of truth is the power of the thought to get itself
accepted in the competition of the market, and that truth is the only
ground upon which their wishes safely can be carried out."
Ever since, the Espionage Act and the Schenck ruling have been slowly walked back, bit by bit. First, the war ended and parts of the Espionage Act were repealed. Whitney v. California in 1927 saw Holmes- though still on the losing end- pick up the support of Louis Brandeis. Hartzel v. United States, in 1944- during World War 2- saw another antiwar pamphlet distributor in front of them, but they overturned his conviction 5-4. Brandenburg v. Ohio in 1969 was the big shift, though, as the nation and feelings toward the military had changed significantly since then. Brandenburg explicitly overturned Whitney v. California and put a gash in Schenck v. United States by stating that the boundary was no longer "clear and present danger" but rather "imminent lawless action". That's about where things have stood ever since as far as the Court is concerned. Still enough to charge Bradley Manning, but anti-draft pamphlets weren't going to get you six-month prison stays anymore.
One last thing. The original 'fire in a crowded theater' quote-that's-more-of-a-paraphrase, though, was never overturned in and of itself. Why? Because there was nothing to overturn in the first place. That was something called dictum. Dictum is court-speak for an aside opinion that isn't to be considered part of the binding ruling.
Even if it's the most famous part of it.