He obviously didn't think he needed your approval. And he's right.
I understand your desire to be consulted--sort of--but he is an adult and can make his own choices, no? And it's a tattoo--so what? If he decided to move to Outer Mongolia without consulting you, I could understand your concern. But we're talking about a tattoo here. Unless the tattoo is on his forehead and reads, "I'm with stupid" with an arrow pointing to the side on which you usually walk, tattoos don't have much bearing on a relationship.
I'm not sure why this bothers you so much. Maybe he never asks your opinion and this is just the latest incident. Maybe you have control issues. Either way, it's his body and he can do what he wants. Being consulted ahead of time is nice but not mandatory, and certainly not something to be upset about, if you ask me. And you did.
If being consulted before he does things is that important to you, I suggest you bring it up to him. He might have no problem doing so, but I don't think he owes it to you or anyone else.
Thanks for the question.