I just recently got one on my shoulder blades (two, if you take
into consideration that they're wings). Pretty bony area,
hence the pain feeling like cat scratches on a nasty sunburn.
I had a death grip on the chair I was sitting in, but in my
opinion, the pain is worth it. I don't know what having one
on the inside of your arm would be like, but I would guess that
because there's tender skin there that you will have some pain.
If you're only getting a small tat, though, you shouldn't
have a problem. Like Liz said, have something to eat before
you go, and bring a bottle of water. I went through two
waters during my session.