No way! 冗談じゃない！
You're kidding! He is not my type. 冗談はやめてよ。彼は私のタイプじゃないの。
Is that supposed to be a joke? それって冗談のつもり？
You're not serious, are you? 冗談でしょう？
"You're kidding!" she said in a surprised tone.　「冗談でしょ」彼女は驚いた口調で言った。