Mine is because I'm a guy who can't spell....and isnt' that creative.
Round about the time I decided to start actually signing up for all these message boards instead of just lurking, I liked the show South Park. Cartmen was my favorite character. So like an idiot, instead of looking up the name to check the spelling, I just assumed it was an 'e' not an 'a'. Thus, the incorrect spelling of the name. By the time I'd realized it was wrong everybody on the net knew my digital self, so I didn't bother to change it.
<-- that is the bad spelling part-->
And my favorite number is 34, because in 1996 I was really into supercross, and Ezra Lusk's number was 34. Ezra was the rider I cheered for, so I added it on the end.
<--that's the non-creative part.-->
Cheers. <-- also a not-very-creative way to sign off.