The butt chip is a computer implanted in your buttock that is the ultimate PDA of the future. You will be able to carry all sorts of data with you at all times. Next up: chair docking bays.

The media made a big deal about a mobster who was convinced that he had a tracking device implanted in his buttock. They very publicly poo-pooed it and made him look like a paranoid fool.

The Devil's Greatest Trick is convincing the world he doesn't exist
--old quote, recently by Verbal (Kevin Spacey), The Usual Suspects

One of Timothy McVeigh's complaints against the federal government was that a tracking chip was implanted in such an area during the Gulf War. Although no evidence exists to support his specific claim, it's true that the US was testing various new equipment and technology, some of which have been blamed for Gulf war syndrome.