The first place to look in determining the scope of harassment law, of course, is the legal definition of "harassment." Speech can be punished as workplace harassment if it's
- "severe or pervasive" enough to
- create a "hostile or abusive work environment"
- based on race, religion, sex, national origin, age, disability (including obesity), military membership or veteran status, or, in some jurisdictions, sexual orientation, marital status, transsexualism [sic] or cross-dressing, political affiliation, criminal record, prior psychiatric treatment, occupation, citizenship status, personal appearance, "matriculation," tobacco use outside work, Appalachian origin, receipt of public assistance, or dishonorable discharge from the military
- for the plaintiff and for a reasonable person.
Note what the definition does not require. It does not require that the speech consist of obscenity or fighting words or threats or other constitutionally unprotected statements. It does not require that the speech be profanity or pornography, which some have considered "low value." Under the definition, it is eminently possible for political, religious, or social commentary, or "legitimate" art, to be punished .
 The definition also does not require that the speech take place in the workplace; even speech outside the workplace can be considered if it creates a hostile environment at work. See Intlekofer v. Turnage, 973 F.2d 773, 775 (9th Cir. 1992) (relying in part on a coworker "telephoning [Intlekofer] at her home" to support a hostile environment claim); Bersie v. Zycad Corp., 399 N.W.2d 141, 143, 146 (Minn. Ct. App. 1987) (relying in part on a coworker "calling [Bersie] at home" to conclude that plaintiff had made a prima facie showing of harassment, expressly applying Vinson); cf. Bartlett v. United States, 835 F. Supp. 1246, 1262 (E.D. Wash. 1993) (finding that two instances of sexually suggestive conduct, including "[p]laintiff receiv[ing] a sexually explicit card at her home from a coworker," did not rise to the level of sexual harassment, but not even hinting that the card was somehow categorically disqualified because it was received outside the workplace); Myer-Dupuis v. Thomson Newspapers, No. 2:95-CV-133 (W.D. Mich. May 9, 1996), reported in Mich. Law. Wkly., May 27, 1996, at 12A. These cases are eminently consistent with the harassment definition given by the Supreme Court: It's quite plausible that speech by coworkers outside the workplace may create a hostile environment within the workplace.
-- Eugene Volokh, 'What Speech Does "Hostile Work Environment" Harassment Law Restrict?'