Thanks for reading and responding, Staci.
In my opinion, a nasty tone by itself is not enough for a defamation case. If you want a definitive answer, though, you should seek advice from a lawyer with experience in entertainment or publishing law, especially if you plan to self-publish.
If you plan to go the traditional publishing route, rest assured that reputable editors and publishers will not take on a work that is even questionably libelous or defamatory. To make sure, they employ fact-checkers. For example, I’ve had essays fact-checked by employees at NYT, WaPo, and Oprah. And I mean every itty-bitty fact.