comfortable in (one's) own skin

Displaying a relaxed confidence in and clear understanding of oneself and one's abilities, especially when presenting oneself to or interacting with other people. Though his girlfriend's group of friends are all older and more established in life, he is comfortable enough in his own skin to have no problem mingling with them at parties. Janet is so comfortable in her own skin that I have no doubt that she'll find her ideal path in life. Is any teenager really comfortable in their own skin, though? All I wanted to do at that age was blend in!