Well, the Kitty part is because I like cats (which is pretty obvious, I think). But all the simple versions of cat, kitty, kitten etc. are always taken everywhere (as there are many people who like us, little kitty bastards), so I needed something more... Sophisticated. And I was listening Blind Guardian at the time. Thus, Blind Kitty was born...
I've actually found out that this name is sometimes taken, too, when there are more people around (initially I was using it on pretty obscure forum, and I was widely considered to be a female because of that - which lead to some hilarious situations, given I was there mainly for PBF RPGs), as people consider young (and thus not yet seeing) kittens to be super-adorable (and the actual badassness of the nick is lost to them, as nobody seems to think 'blind warrior monk that is a fluffy badass kung-fu master', and rather just 'little blind kitty that needs to be taken care of'). And I'm sometimes going by other names, because of that. I think I need a new nick, actually, to keep more consistency because of it, but it seems like too much hassle, especially considering that I usually can't change the nicks whenever I already have declared them (as for example, on this forum).
As an example, in Tribes: Ascension I go by the CarbonCat. It is taken even more often than BlindKitty, but somehow it was left free when I made my account there. But if I'm not mistaken now, BlindKitty was actually free on Battlelog when I made myself there. It's pretty complicated stuff, those usernames.