This is an entry I posted in the Oldunreal version of this thread, modified for a different audience of course.
Like everyone else on here, I was young (maybe about 12 years old), ignorant, and thought naming everything "killer" was cool. And me being a rabid Unreal fan, I stuck 'Skaarj' at the end because I had no originality, thus making "Killer Skaarj," with the space. Then while playing in an Unreal 1 server, I somehow noticed that my name had an underscore, I don't know where it came from, but that prompted me to go back into the Player Settings menu and put an underscore between Killer and Skaarj. But that wasn't enough for me, because I went ahead and added '@' signs to it to make it "Killer_Sk@@rj." Then over the years as I matured I removed the @ signs, then recently (maybe like 3 years ago) I removed the underscore as well.
I use this nick on most gaming sites and message boards, but more recently I've been using "KronoJovia" for MMOs, which is a malformed portmanteau of the Greek titan Cronus (known as Saturn in Roman mythology) and the Roman King of all Gods Jove, AKA Jupiter. Astronomy FTW.
Fun fact: DeathPax, a well known U1 server admin and leader of the KSA clan, had a modded (and marginally annoying) Skaarj on his server called a Killer Skaarj. Not only that, but his clan, KSA, is short for Killer Skaarj Assassins. Naturally he thought I borrowed the name from him, which made for some pretty awkward moments.