What kind of a screen name is that? Well, it turns out that "Chris", "Christopher" and "Thomas" are pretty popular names. Trying to turn them into an email address that no other "Chris", "Christopher", or "Thomas" has used is pretty hard (cthomas, thomasc, christhomas - if you can think of it, someone's already claimed it). I also try to be non-controversial, so the combination 'christ' is out. The company at which I currently work, in their corporate wisdom, tried to saddle me with "christho". I threatened to quit if they didn't change it (say it out loud to figure out why).
The only alternative was something arbitrary. Rather than be completely random (like lel223xz), I thought I should pick something that had meaning to someone. A 'Youkai' is a half-animal sprit, half human being from a popular japanese manga/anime series called Inuyasha which I happen to like. It's a bit geeky (the anime audience tends to be heavily weighted that way), but it is short and easy to remember.