I had one put on my ribcage, it hurt like a mother fo.
Ribcage, eyelid and maybe the front side of the neck
wherever your skin is most sensitive...
also depends on size and saturation of tattoo. as well as how thick the needle being used is...
Probably where the bone is close to the skin.
my shoulder blade hurt like a b1tch. 1 hr 45 mins of it too. arms are easy
Probably on the private area.