Happiest moment in your entire life? Biggest disappointment? A thing you'd change about yourself.
Happiest was getting into uni. Best decision I ever made. Biggest disappointment was college. It wasn't much different than school. I'd be more talented in various different activities (sport, art etc).
I've used it since around the age of 12. Myself and a friend used to play a game called Splinter Cell: Chaos Theory, and one day he suggested the username (when my younger brother took up online gaming, he became SoulSharD, so it's weirdly enough a family thing). The capital D originates from a glitch in the game where you could delete your account, reactivate it and whilst doing so change one of the letters to upper case, which resulted in you becoming immune from bans.
Thats suprisingly quite interesting. When I made mine a younger kid chose it and threw a tantrum when I wasn't too keen on it. Recently she asked me why I had such a silly username.