Seriously. What's with that.
it's like calling chips as chippy
it's about like having a friend named john and calling him johnny.
-n is like -chan.
Kagami pig
-n indicates cuteness when added to a name. Read azumanga daioh for the info
It's like -chin. It's a cutesy -chan.
what everybody else said, ALSO to annoy Kagami, like the whole tsundere business. It's all because Konata is convinced her life is an anime (oh the irony) and that Kagami is the tsundere character in this anime (and I repeat- oh the irony). So yes, it's all part of this huge, semi-ironic, joke.