1. Knowingly false statements of fact about a person are indeed constitutionally unprotected, whether they injure the person’s reputation (and are thus libel or slander) or would simply be highly offensive to a reasonable person (and are thus actionable under the false light tort. But that is so only when a reasonable listener would perceive these as factual assertions, not as hyperbole or as statements of opinion.

Thus, for instance, say that A asserts that B is guilty of “blackmail.” Blackmail is a crime, and accusations of crime are generally actionable libel. But if in context it is clear that the word is “rhetorical hyperbole, a vigorous epithet used by those who considered [B]‘s negotiating position extremely unreasonable,” then the accusation is constitutionally protected opinion — it is basically an assertion that B’s accurately described conduct is morally similar to blackmail, a statement of opinion (and perhaps clearly understood hyperbole). So the Court held in Greebelt Coop. Pub. Ass’n, Inc. v. Bresler (1970).

Limbaugh’s saying that Fluke’s testimony “makes her a slut” and “makes her a prostitute” falls into the same category: Listeners would understand is as “rhetorical hyperbole, … vigorous epithet[s] used by [Limbaugh,] who considered [Fluke’s advocacy] extremely unreasonable,” an assertion (however logically unsound, in my view) that Fluke’s demands are morally similar to a prostitute’s insistence on getting money for sex. That is a statement of opinion and constitutionally protected.