Tattoos placed over bones and tendons (spine, neck, back of ankle), on body parts with relatively little padding (feet, hands, joints), and anywhere with loads of nerve endings (nipples, fingers, face) will be the most painful.
Chopsticks task - Use two sets of chopsticks or something similar on each nipple like in the picture above. For added pain, tie the end of the chopsticks to something static and stable in front of you and pull back, stretching your nipples.
