I remember messing around in some chat-rooms back around 1997-1998. At the time, I created a username based on a character out of a book series I was reading at the time. The problem was, the book series was quite popular, so I found that it was impossible to keep the name from one chat-room to another.
Similar to Urwumpe, I didn't want a username like Name197272, so I tried to invent a new name that had absolutely no meaning so that no one would ever use my name again. I wanted it to be as short as possible, but long enough so that I wouldn't have to add random numbers/characters on the end of it when signing up for forums and what not.
While staring at my computer screen, the word pixel popped into my head. After messing with a few letter combinations ... blixel was born.