其实最流行的说法应该是：我是来打酱油的。

我不在乎。

说得俗一点是 “关我蛋事” 虽然有点不文明，但有时候符合语境。。呵呵

There is no difference among three sentence actually. that's right whatever do you want to use. 1，I dont want to know your business(you can say: 你的事情与我无关，或者我不关心你的事情) 2，I dont care which method do you want to use in chinese(you can say:我不在乎/不管你用什么方法学汉语)

我不在乎。