Beginning January 1 all United States issued passports will include a little RFID chip that has all of your delicious information embedded. The passports with said RFID chips are clearly marked on the front, and the RFID chip is in the back. There is only one fool-proof method to destroying the RFID chip to prevent those RFID-hacking hobos from taking your information: bash in the chip with a hammer. This is really the only method that won't destroy the rest of the passport. Some of the other methods that definitely won't work includes washing, microwaving or stuffing the passport down your pants (sorry, Jason, RFID signals penetrate the pants).
Oh, I forgot to mention: tampering with a passport is punishable up to 25 years in prison, so proceed with your own risk.