>I thought there were rules like not yelling "FIRE!" in crowded movie theatres etc.
>
>Steve Martin once posed the question of whether it was OK to yell 'MOVIE' in a crowded firehouse. ;)

All kidding aside, a brief Google search turned up 5 main categories in which free speech is limited, i.e. not just libel/slander:

http://www.philartalliance.org/Lesson1.pdf

That document may not be exhaustive; for example it doesn't seem to address verbal harassment, unless that fits under the 5th category.