Back when I was in Grade 10 in highschool I was trying to make a hotmail account and every name I could think of was already taken. One night my parents took me to one of those "gifted children tests" where they put you through a bunch of test to try to identify any special talents or mental dexterity one might have. One of the tests had a this random word generator which would create words you needed to pronounce. "centizen" was one of the words and the only one that I really liked, so I took that as my user name, thinking I wouldn't be able to get much more unique than that.
Funnily enough, I've actually met other centizen's online who got their usernames the exact same way.
And my avatar is the cover to Dream Theaters Metropolis Pt2; Scenes From A Memory. One of my favorite albums from one of my favorite bands, it's essential listening for any prog metal fan. This CD art, is one of my favorite pictures, all of separate images or "scenes" if you will (all referencing event in the album), coming together to form a bigger picture.