Turtle head
Growing up, we were all big fans of Teenage Mutant Ninja Turtles, and we can only assume this person was as well. He probably wanted to pay tribute to this magnificent animal, and since he was bald anyway, it seemed like the perfect spot to get the shape and essence of the animal.
The only problem with such a tattoo is that hiding it, if you ever get tired of having a giant turtle covering your head, might be a challenge. Sure, he could always wear a hat, but that won’t cover the little turtle head and feet poking out of the shell.