Check out these Japanese teeth tattoos. Made out of a thin film and affixed with a non-toxic, edible adhesive, they stay on the teeth for up to a week but can be removed sooner.
Themes range from simple pattern designs, text, and insects like the ladybug tattoo in one of the photos above. I guess if you rock one and someone tells you that you got something in your teeth, you can probably just reply: "Yeah dude, I know." [Design You Trust]