I was born with a condition known as pectus excavatum, which has serverly damaged my self-image. Pectus excavatum is a condition where your sternum grows inwards creating a "depression" in your chest, it can be mild to severe. Mine is probablly considerd mild. But whenever I have my shirt of in public, I get asked about it. I got teased about it in school.
This has really messed with me psychologically, so if you ever see someone with it - be polite.