Books of advice come in many forms: financial, spiritual, physical, philosophical. Novels too are books of advice, if read in a certain light. Eve Babitz understood, for example, that part of Colette’s greatness is that you can open her novels anywhere and “brush up on what to do.”

There are only two advice books I’ve read more than once. One is Tom Hodgkinson’s “How to Be Idle” (2004). Its title is self-explanatory. The other is J.P. Donleavy’s “The Unexpurgated Code” (1975). Its title is less so. Donleavy’s book is a sendup of the form that happens to be, possibly, the funniest book ever written.

“The Unexpurgated Code” turns 50 this year. It has dropped from sight, and yet here we are at a moment when the world could use it. It’s a book to turn to when you need a little pick-me-up. It is Bolivian marching powder for the spirit. The table of contents alone is more happily anarchic than most books in their entireties. Here are a few of Donleavy’s 270 topics:

“Upon Placing the Blame for Venereal Infection,” “Upon Embellishing Your Background,” “Upon Being Unflatteringly Dressed in an Emergency,” “Upon Your Spit Landing on Another,” “Upon Fouling the Footpath,” “Upon Heaping Abuse on the High and Mighty,” “Upon Being Exorcised” and “Upon the Nearby Arrival of a Flying Saucer.”

Donleavy is best known as the author of “The Ginger Man,” his tumultuous 1955 comic novel about Sebastian Dangerfield, an American student living in Dublin. (Sample sentence: “All I want is one break which is not my neck.”) He is also the author of many other novels, plays and books of stories. His novel “A Fairy Tale of New York” (1973) inspired the title of the song by the Pogues and Kirsty MacColl that helps make Christmastime bearable.

Donleavy was born in Brooklyn, to Irish immigrants, and grew up in the Bronx. He was the son of a firefighter. After serving in the Navy during World War II, he spent the rest of his life in Ireland. He was rarely photographed in anything other than layers of tweeds, so that he resembled a walking advertisement for 18-year-old Tullamore Dew.

Battered copies of “The Unexpurgated Code” pass among admirers like samizdat. The reason isn’t merely that it’s funny. The book clocks the absurdities of human conduct like few others. It takes note of the chutes and trapdoors and ladders and ejection seats involved in all human discourse. It says: We’re all miserable bipeds struggling for a bit of breathing room, so you might as well have a sense of humor about it all.