that is so, so cow vagina! no really, 真牛屄。
This is yet another example of a slang phrase that makes no sense. 牛 [niu2] means cow, and 屄 [bi1] means vagina. That's right. 牛屄 means cow vagina.
But in China, at least in Beijing, it means 'da shit' or 'awesome' or 'really cool' or 'hardcore' or similar.
It's sort of like saying 'that's the shit' in English. As in, that [insert noun] is 真牛屄!!