When should I not get a tattoo? What about illness?

You shouldn’t get a tattoo if you’re drunk or high (and most tattoo shops have a policy in place about this; they’ll refuse to tattoo anyone who appears to be drunk or high or just plain stupid). The other reason for not getting a tattoo is if you’re not sure. Wait until you do feel sure or just don’t get one. This is not a good thing to feel ambiguous about. There are no specific medical considerations, but use your common sense. If you’re sick, wait till you get better.