Katai
Is a Japanese word for "Hard", especially in the male genitalia. Or if you're watching Hentai, then you know what I mean...
これ わ かたい お (Kore wa katai o) - This is Hard
katai
it means anything and everything, whatever you want it to mean and can be a substitute for any word, even if they are opposite in meaning
OMG that shirt is so katai I love it!! or OMG that shirt is so katai I hate it!