Scar's brother. The tattooing. The Rolling Stones. No, wait, not the Stones.
I will accept that perhaps he is ambidextrous, or at least very skilled, and can tattoo his own arms, legs, and chest. But who tattooed his back? It wasn't Scar, he was all "..the hell?!" when he saw his brother like that. And alchemy is supposed to be mightily forbidden in the Ishval religion, so it couldn't have been one of his buddies... could he have transmuted a tattoo onto his back? Perhaps his back isn't tattooed, it's just done with a Marks-a-lot. In which case, he could have drawn the design on contact paper or something and then applied it to himself. OK now I'm just being silly.
The other question that keeps me up at night is what Scar's real name is. That one doesn't vex me as much, though.
Oh, and thanks everybody for giving me some great ideas for my layout. I ended up not making it beautiful, though, and instead just made it weird as hell. Check it out, if you dare.