1、What did you say?你说什么。
2、具体场景：
如果是两人去吃饭等场景，需要一人做出决定，如
A：Would you like to eat Chinese food or Japanese food?
B：its up to you. （你做决定吧，你说吃什么就什么）
what are you talking about? 自己加强语气.一般的话,what are you saying? 就行了.
I have no idea what youre saying!不知道有没有拼错!可是如果伱要惊讶的话,就是这句了!