Unless you have a lot of padding in that area it is extremely painful. anywhere that is boney hurts. A little story for you. A number of years ago I was in a TA2 parlor. a few artists worked there. Anyway a young girl goes in ahead of me and she wanted a name, on her upper chest (her 1st TA2). . Near the shoulder. So she shows the guy where. She wanted it in an area that would make it go across her collarbone. He tried to talk her out of it and move it down a couple of inches. He tried this 4 times, but she insisted. So he starts the work. after about a minute she lets out with this horrifying blood curdling scream. You would think she just came across a gory murder scene. That was as far as the TA2 went. She had to sit for about 15 minutes before she composed herself enough to leave.
Yes it hurts. I have a small tattoo there, it's a small one, I'm not skinny but it hurt like hell. I heard that the arm is one of spot that hurt the less. It hurt and you don't want the artist to mess up so you barely breath, not an easy spot.
It depends on your weight, it hurts more in areas where there is less muscle and tissue, it would be like trying to write on concrete with a pencil.
My dad got his done on his ribs, he's a bit on the skinnier side and he says it hurt him like hell, and by his "screams" i believe him. He did manage to get it done after he passed out. When I got my arm, back, and ribs tattooed it hurt the worst on my ribs.