This, from chillingeffects.org (FAQs about defamation), is hilarious.

Question: What is a statement of verifiable fact?

Answer: A statement of verifiable fact is a statement that conveys a provably false factual assertion, such as someone has committed murder or has cheated on his spouse. To illustrate this point, consider the following excerpt from a court (Vogel v. Felice) considering the alleged defamatory statement that plaintiffs were the top-ranking 'Dumb Asses' on defendant's list of "Top Ten Dumb Asses":

A statement that the plaintiff is a "Dumb Ass," even first among "Dumb Asses," communicates no factual proposition susceptible of proof or refutation. It is true that "dumb" by itself can convey the relatively concrete meaning "lacking in intelligence." Even so, depending .., it may convey a lack less of objectively assayable mental function than of such imponderable and debatable virtues as judgment or wisdom. Here defendant did not use "dumb" in isolation, but as part of the idiomatic phrase, "dumb ass." When applied to a whole human being, the term "ass" is a general expression of contempt essentially devoid of factual content. Adding the word "dumb" merely converts "contemptible person" to "contemptible fool." Plaintiffs were justifiably insulted by this epithet, but they failed entirely to show how it could be found to convey a provable factual proposition. ... If the meaning conveyed cannot by its nature be proved false, it cannot support a libel claim.

Makes me miss Journalism classes and free speech debates over Hostess cupcakes in the newsroom. The good old days!