Edit: I wanna get a tattoo that starts from my waist and leads up to my rib cage, whats the pain like for something like that?
As others have already said, ribs are probably on the upper scale of the spectrum.
Regarding the pain, it's obviously wise to assume pain and if you don't suffer too much on the day then it's a bonus. Before I had my first I worked myself into a real panic about how much it would hurt. I don't have a particularly high threshold for pain or anything and I'm not being macho about it, but it didn't hurt me too much at all. On the contrary, I actually quite enjoy the sensation of having them done. I can see how people find them addictive.
Well, I've now got 4. All on the arms though, admittedly I've yet to have anything done in a "red zone" for pain. I want something across my chest which I guess will be the big test for that.
For me the biggest thing was just getting a concept of what it feels like to be in the chair and what the needle actually feels like. Now I know that, I think if be in a better position to deal with pain when I get some done in worse areas.
I'm sure you know this anyway buy always pick the work you want based on why and where you actually want it. Don't pick based on where hurts the most or least. If you want the work doing on your ribs then go for it. The pain, to whatever degree you feel it, will be temporary, but you'll get the chance to love the awesome piece you end up with forever.