It's interesting to look through the reader reviews for this book; I don't know that I've ever seen a book veer as wildly between 1 and 5 star reviews. The lower ratings often express dismay and outrage at the book's subject matter, which, given its title, may strike one as a bit silly.
"This book is about butts? What trash!"
Not only is this Australian book about butts (the title originally used "bum"), but the word "butt" is in virtually every sentence. If you or yours enjoy scatological Aussie humor, you'll love this. As a middle school teacher, I've seen this book in so many hands, I felt obligated to read it. I may have regretted my decision when the book's main character and his pal ride an exploding butt pimple, but I stuck in there.
So to summarize: The Day My Butt Went Psycho is funny, and it's about butts. Be warned.
Also recommended: The Big Book of Boy Stuff