Greg Fitzsimmons appears at the Palm Beach Improv through Oct. 30. (Ethan Miller / Getty Images)

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For Greg Fitzsimmons, the idea for a memoir came from a single letter.

Fitzsimmons, who will be performing standup Thursday through Sunday at the Palm Beach Improv at CityPlace, was hired to perform at a high school prom in Oklahoma. Even though he was extremely well-received, his agent received a letter from that school’s principal.

“The letter said that I’d destroyed the morality of the whole town,” Fitzsimmons said. “And I decided to take the letter and read it on stage. More people laughed at the letter than my words, and I figured out, this is why we save these letters.”

The good news for Fitzsimmons is that his mom saved all of the letters she’d received while he was growing up – notes from teachers, principals, police reports and more. These little bits of history became the frame for his book Dear Mrs. Fitzsimmons: Tales of Redemption from an Irish Mailbox.

“It was kind of curious my mom would save (the letters),” Fitzsimmons said in a telephone interview. “But I found that it revealed something about where we came from, and that it felt like I was connected to something bigger when I found this collection.”

The book promises to be a very open and honest recollection of what he called the “first half of his life” – it’ll be out on Nov. 9. And Fitzsimmons said he couldn’t possibly back down from any part of his life for this book, which includes the struggles he had relating to his father, New York-area radio personality Bob Fitzsimmons, and the battles with authority that grew out of that problem.

“I think so many memoirs out there are fictionalized too much,” Greg Fitzsimmons said. “In this case I sort of felt like I was showing my work – with a police report or a note from my teacher when I got into trouble. So much of dealing with a mid-life crisis is to look back at what you’ve done and learn from them while letting it all go.”

Fitzsimmons continues the story beyond his mom’s saved letters, openly discussing his behavior as he began working in stand-up comedy, including stories about drugs, alcohol and sex. Some of the stories have ended up in his act, stories that might cross the line for many people to talk about.

“My criteria for what I’d talk about on stage would be to ask myself, ‘Would I be embarrassed if I told this on stage?’ ” he said. “If it’s a true story, there’s going to be a tension in me when I telling it, where it becomes funny for people. Everyone’s got something in their past that they don’t want anyone to find out about. And you can’t achieve clarity without coming to terms with that stuff.”

These days, Fitzsimmons has a successful career as a stand-up, appearing on shows like VH1’s I Love The series and late-night talk shows. He also has a show on Howard Stern’s Sirius-XM station, and produces podcasts weekly.

He also leads a much different life now – he’s been sober for two decades, and has kids of his own (whose letters he also includes in Dear Mrs. Fitzsimmons). He said one of the major themes of the book is that he survived the incidents he, and the letters, detail.

“A lot of the book is about that – not crossing over the edge, losing friends who weren’t able to pull back,” Fitzsimmons said. “Friends who died in car crashes. It’s about how random things are and how lucky I feel.”