The Very Unsafe Book for Boys, Vol. 3: Boxing is a book in Fable III written by Konan Wiggledung.
Fast travel to Finkelhouse Farm, the the first cabin in the small circle of homes found near the centre of the Silverpines forest. Walk to your right, around the cabin, and find the book on top of the nearby crates.
Boxing is a wonderful activity for boys. The first thing you'll need, besides a mate willing to let you hit him, is a pair of boxing gloves. These can be purchased from a leather craftsman or stolen out of the locker of a boy you don't like. The idea behind boxing gloves is twofold: to protect the boxer's hands, and to minimise injury to the opponent. At least, that's what you should tell your mum when you ask her to buy them for you -- she'll think you sound very mature. Be sure to use that word 'twofold', as well; that will really impress her. Anyway, the real point of boxing gloves is they allow you to hide large, heavy metal weights which will really knock your opponent's lights out. That'll teach him.