My username has always been a bit of a strange topic. Long ago, I was introduced to role playing. I took to it quite rapidly, partially because my life at the time was bringing me down.
I was informed of a semi-secret RP board on GameFAQS, and I was asked to join. I knew of the site, that's where I went for my info on games. But I first had to register before I could post, so I decided to pick a username that I'd be able to use in the RP as a name for my character. Since my character was a teddies experiment with chainsaws for hands, and various other inhuman(er, insquirel?) things, I picked a serial number type name.
I didn't end up joining said semi secret RP board, but I found a username that was never taken and suited my blend of madness well.