This is not as easy to answer as it might seem.
To start with, I never have had much of a nickname. I mean, what's short for "Sean"? Not much, as it turns out.
I did have a friend in Middle School who at first thought my name was "Sam." I have used that from time to time, but it never really stuck after about Eighth Grade. It is engraved on a beer mug I used to keep at my favorite bar in college, but that's a story that really doesn't bear the retelling. Suffice it to say, the name still didn't stick.
Many people who don't know me well call me "Scott" for reasons I can't exactly explain. But that doesn't really work for a nickname.
When I was a kid, my father like to play complex word games. The older I get, the more I realize how much he liked to play with words. One of the games was to call me "Seanibus" and my brother Evan "Evaninski." I assume this is because the first sounds Latin and the second sounds Russian, but I have never asked him what it was supposed to mean or where he came up with it. I probably should ask him, but I think some mysteries are better left unsolved.
So when I needed to come up with a screen-name for a movie-related discussion group many years ago, I remembered "Seanibus" and tried it out. And it stuck.
Not that it hasn't caused confusion, of course. People seem to find it impossible, for example, to get my Web address right on the first hearing - s-e-a-n-i-b-u-s-dot-com. Sounds OK to me, but apparently I am in the minority.
And lately I have been chatting on various home brewing and beer-related websites, where people seem to think that my screen name means "Sean IBUs," as in International Bitterness Units, the somewhat vague measure of the bitterness of the beer, usually produced by adding hops. Despite my love of a nice, hoppy beer, I assure you, Seanibus has nothing to do with IBUs.
And my now more or less official nickname now comes with my more or less official avatar:
What I would look like in South Park.