https://arstechnica.com/tech-policy/2019/08/patent-troll-sues-over-patent-troll-label-loses/

Automated Transactions Limited (ATL) is a small firm known for its aggressive enforcement of broad patents related to automated teller machines. Numerous critics labeled ATL a patent troll, and in 2016 the firm sued several of them in New Hampshire state courts, arguing that the label was defamatory.

On Friday, the New Hampshire Supreme Court dismissed ATL's lawsuit. To win a libel lawsuit, a plaintiff has to prove that a statement is both false and defamatory. A statement of opinion can't be proven false, and hence can't be the basis for a libel claim. New Hampshire's Supreme Court ruled that calling someone a "troll" was just such a statement of opinion—and so someone can't be liable for calling someone a troll.