Well... (for lack of creativity) Mine is the first 3 letter's of my first & last names (FRE & TAI) and 03 was my last year at Uni...
Very boring & I don't really like it but it's stuck with me on so many forums that it would be a huge thing for me to just go & change &
the name which has kinda just built it's own (very small) reputation.
I originally wanted to go with something that had Fred in it but all the ones I chose were already picked so my creativity stalled after a good 3 hours of trying to figure something out & I just went with this one.
P.S. I don't mind if people call me Fred. I actually prefer it.