-The easiest way to kill an RFID, and be sure that it is dead, is to throw it in the microwave for 5 seconds. Doing this will literally melt the chip and antenna making it impossible for the chip to ever be read again. Unfortunately this method has a certain fire risk associated with it. Killing an RFID chip this way will also leave visible evidence that it has been tampered with, making it an unsuitable method for killing the RFID tag in passports. Doing this to a credit card will probably also screw with the magnetic strip on the back making it un-swipeable.Link, Link to RSS feed for Little Brother Instructables
-The second, slightly more convert and less damaging, way to kill an RFID tag is by piercing the chip with a knife or other sharp object. This can only be done if you know exactly where the chip is located within the tag. This method also leaves visible evidence of intentional damage done to the chip, so it is unsuitable for passports.
-The third method is cutting the antenna very close to the chip. By doing this the chip will have no way of receiving electricity, or transmitting its signal back to the reader. This technique also leaves minimal signs of damage, so it would probably not be a good idea to use this on a passport.
-The last (and most covert) method for destroying a RFID tag is to hit it with a hammer. Just pick up any ordinary hammer and give the chip a few swift hard whacks. This will destroy the chip, and leave no evidence that the tag has been tampered with. This method is suitable for destroying the tags in passports, because there will be no proof that you intentionally destroyed the chip.
See also: HOWTO Screen-print a tee