I remember the commercials for that episode promising we'll find out how Jack got his tattoos and thinking "wow, people actually care about that? When we have an island filled with monsters and polar bears and hidden forest people who steal your children and numbers you have to enter to keep the world from ending? People care how and why Jack got a couple of tattoos?" I had always just assumed he got a bit adventurous one night back in his college days. Didn't really see why it needed to be made into a plot point.