RokofAges75 is all Brian, since he's my favorite. It's a play on his "rock of ages" tattoo, using his nickname B-Rok, and 75 for the year he was born. Nothing too unusual, but I've had it for about as long as I've been writing fanfic, so it's a staple!
Here's another question: What was the first username (or email address) you used for fanfic?
I got a new email account just to use for fanfic when I got my first story hosted. It was ktbspa5@hotmail.com LOL. The screenname that I used for a lot of things, like AIM, was JRok8540 - another play on B-Rok, except J wasn't really for Julie as much as it was for Josh, this guy I had an obsessive crush on throughout junior high and high school. 85 is the year I was born, and 40 was his football number LOL. He's the one I made myself married to in the suspense self-insert story I mentioned in my answer to the self-indulgent story question. I had tons of AIM screennames, but I think I created the RokofAges75 one later that year (2000) and have used it for everything else BSB- and fanfic-related since.