*sigh* You most certainly can yell FIRE in a crowded theater. . .you may be morally obligated to yell that if there is actually a fire.
What you cannot do is use the cover of "free speech" to harm others: slander, libel, or yelling FIRE in a theater.
What you cannot do is use the cover of "free speech" to harm others: slander, libel, or yelling FIRE in a theater.