Comment on it in writing: I am both the best and the worst child in the family because I am an only child

As I get it - being the best child in this situation means being the only joy for your parents - they will not compare you with your brother/sister, all their attention and time will be given to you. Being the worst probably means not meeting your parents ' expectations or being spoiled child, taking many things for granted, as you consider yourself the center of the universe