Nǐ yǐwéi nǐ shì shéi？

你以为你是谁？

Who do you think you're?

Notes:

你(nǐ): you

以为(yǐwéi): to think

是(shì ): to be(am, is, are)

谁(shéi): who

Example:

A：你以为你是谁！

      Nǐ yǐwéi nǐ shì shéi？

      Who do you think you're?

B：我是的老婆！

     Wǒ shì nǐ lǎopo!

     I'm your wife.