>Here's how you do it.
>
>Take a syringe. Open his toothpaste. Put the tip of the needle
>*just* into the middle of the toothpaste opening. Inject.
>IMPORTANT: smooth over the end of the toothpaste with your
>finger so that it looks normal when he opens the tube.
>
>He'll put the toothpaste onto his brush, not think for a
>second that anything would be wrong, and start brushing. By
>the time he tastes the ink, he'll have done a scrub or two
>onto his teeth. Which is really all you need.
>
>If you're worried about your ability to not accidentally have
>the ink reveal itself when he squeezes the paste onto his
>brush, then buy a couple of practice tubes and practice with
>food coloring. (That's how this prank is normally done. Tattoo
>ink would really fuck his shit up, though.)