I used to go by "NeonUltima" when I played on Pokemon NetBattle back in 2004. If I remember correctly, I chose this because I was a fan of neon colors and Ultima was my favorite move from the Final Fantasy series.
When I first started playing TF2 in '07, I kept going with this name until a day when I was pubbing and ran into YouMustRecover. For some silly reason I assumed his name was a command to the players on his team so I went medic and changed my name to "YouMustDestroy". He introduced me to competitive TF2 soon after and little did I know, having similar names with someone who was even relatively known was a problem. And now any time dchow tries to say something insulting, he brings this up.
So then I had to change my name and seeing as Kirby 64 is one of my favorite games ever, I decided to be unoriginal and name myself Kirby.