A tattoo on the part of the body between the scrotum and the anus.
"Hey Brad! While you're down there, check out my taintoo."
by Brian Freaking Jones April 05, 2008
a tattoo on the perineum
Burt was totally hammered last night and Steve and Morty talked him into getting a taintoo that says "Keep Going."
by Decidedly So June 03, 2007