Context: Sora stayed over at Ema's house. Ema quit her job two weeks ago and has not cleaned up her house since then.The morning after his stay, Sora says this during breakfast:
At first I thougt 「ナイ」was more or less used to emphasize 「汚い」; however as Ema, comments (not in dialogue, but as narrator) with:
I kind of have the feeling that 「ナイ」has meaning on its own. From what I can guess it is meaning-wise related to 「汚い」and probably very casual.
In any case, what does 「ナイ」mean here and in general？