If your advertising blowhard is new to the game, you're going to want to get he/she a copy of Malcolm Gladwell's original work of genius The Tipping Point. It's really all they need, obviously, but if that sly fox already has it then go for his latest, What the Dog Saw. Having any Gladwell book on his/her desk will give your friend cache.
For the slightly more advanced piranha, you should go for Eating the Big Fish. It's not the size of the fish in the fight...right? Unless you're a prawn flossing the teeth of a Blue Whale, that is. Unless you're a prawn filled with POISON! See, so much to contemplate. I don't really understand what this book is about.
For the slightly morally distressed ad man, pick up a copy of one of Jane Goodall's treatises. Try her latest, Hope for Animals and Their World. or Freud's The Ego and the Id. It'll help your poor compromised friend understand our common humanity or at least hear out the subconscious that's telling them that they should get the fuck out of the industry. Just don't think about handing over a copy of one of Dr. Seuss' oeuvres. They don't need any further introduction to their inner child.
Finally, if your advertising friend has really had it and is ready to go make hand painted bowls in Tofino, they're probably ready for a heart warming blue collar success story like Big Sid's Vincati(father-son bonding! Large machines that go ROAR!). The Pleasures and Sorrows of Workis a good back-up choice.
Then again, a really large bottle of scotch might be the best idea. Two large bottles of scotch, while you're at it.