Suicidejim was a name I gave to one of the guys on my team from 'Worms,' who just used various kamikaze techniques. I reused the name again later for a stick figure who wore a top hat and whose escapades were created during the times I should have been paying attention in maths. Afterwards, i just got into the habit of using it as a username, because nothing else sprung to mind, and I've always enjoyed the sound of it. I mean, suicide, although an awful thing, is a very nice word to say. It flows so well. The 'Jim' at the end just provides a nice little contrast at the end, as it's shorter and sharper.
Recently, however, it's become a little bit of a nuisance, since I have people A) assuming I'm suicidal, which is very rarely true and B) that my name is Jim. It is not Jim.