Most Helpful Guy
As a professional tattoo artist I do not recommend the ribs for a portrait tattoo. The area is very uneven, and will distort your pets features. Its also a very painful spot. So if you make a sudden movement because of the pain, you can really spoil it. If you're going to get a pet's portrait, then pic a smother area like the back, or thighs.
Most Helpful Girl
It's your body and there's nothing wrong with it. Some might think it's tacky, but tattoos are supposed to mean something to the person getting them, and what better tattoo to get than something that was special to you. I'd just make sure it's designed and placed tastefully.