You are joking, aren't you ?

你们在开玩笑，是吗？

If you are joking then this post was rather funny. If not, then I pity your life.

如果你的这个帖子是开玩笑,那挺滑稽的, 如果不是, 那我真可怜你这条生命.

You are joking, Lizzy. This cannot be! -- engaged to Mr. Darcy! No, no, you shall not deceive me. I know it to be impossible.

你在开玩笑！丽萃。不会有这种事！跟达西先生订婚！不行，不行，你不要骗我；我知道这件事不可能。