I had a thought earlier today that I thought might be worth sharing. Just an observation taht may or may not be accurate. I expect the more knowledgable board members might be able to confirm whether I'm right or wrong.
Anyway, the question occured to me today "How did Iceburg get "Franky" from "Cutty Flam" (When Franky heard of Iceburg's 'death' he thought of Iceburg giving him the nickname). Upon thinking about it, I got an idea.
"Franky" is a shortening/play on "Flam-kun."
I've seen a couple of examples of this in other manga. In Sgt. Frog (Keroro Gunso) one of the alien frogs refers to the main boy, Fuyuki, as Fukkie. He also calls one o the main girl characters, Momoka, Momochi (as opposed to Momoka-chan). Also, in Angelic Layer, the main girl Misaki gets christened with the nickanme, Misakichi.
It seems to be teh same concept, combining a name with part of the suffix/honorific that would normally go to it. So "Furamu-kun" became "Furankii."
At least that's my guess. I'm curious if anybody's noticed/thought of this before now.