The most painful place to get a sternum tattoo would be directly over the bone itself. As this area is particularly bony, the needle will more easily penetrate the skin and cause more discomfort than elsewhere on the body. It's best to avoid getting a sternum tattoo if you are sensitive to pain or have any underlying medical conditions that may be a risk factor. That said, most people find that the pain is manageable and worth it in the end. The best way to reduce pain when getting a sternum tattoo is to take deep breaths and relax throughout the process.