It kind of started as a private joke.
In the mid 80's the company I worked at used the common user-name convention of prefixing the last name with the first initial, like the Dilbert joke about Brenda Utthead constantly asking to have her user name changed. So my username was "dwise".
We also got a few of the first-generation Macintoshes (which were brand-new at the time) to do some of our documentation on. Each of us had a system diskette (no hard disk on those suckers) and a data diskette (3.5-in and colored, just like in Star Trek! Cool!) and we each labelled our diskettes with our username. Then my data diskette filled up and I had to expand to two data diskettes. I labelled the new one dwise2 and went back and labelled the first one dwise1. Then one day a co-worker read the label of my first data diskette and started laughing.
A few years later when I signed up for AOL and it wanted a screenname, I remembered that incident and used dwise1.
Quite unintentionally on my part, a few creationists had chosen to try to pick fights with me because of my screenname. More notably, when I emailed Kent Hovind for clarification on his solar-mass-loss claim, in order to weasel out of supporting his own claim, on two separate occasions he tried to pick a fight with me over "dwise1".
Edited by dwise1, : added explanation that that was when Macs first came out