My name's Dan. Back in freshman year of college, through a story that's a little too long and uninteresting to recount here, I got the name "Daffy Dan," like Daffy Duck. Pretty soon, all my RL friends were calling me Daffy, and I was answering to it as reflexively as I did to my own name. My old (OLD OLD) nickname was ViperEye, but it was a tad... juvenile for me. So I started using a new one, based on my nickname. Daffy -> Daphinicus.
You may all consider yourselves enlightened. And about 45 seconds older. Sorry.