I guess I'll start.
The Sable part came from my Sorta-but-admittably-not-really-original fan character, Sable (the same character in my profile pic) which originates from a sort of story thing I came up with for myself sometime last year.
The "Xeno" part come from my current NNID, Xenobreeze, which was meant as a simile to my previous Gamer Nickname, Starwind. (star referring to Geno, and wind referring to Klonoa). The "star" part was re-worked into "Xeno" because I had recently played Xenoblade Chronicles...and loved it.
EDIT:As for how SABLE got his name...well, you know Mabel and Sable, from Animal Crossing?...Yeah, I have pretty basic inspiration.