应该是"I'm just pulling your leg.",即我其实在逗着你玩.
如果说成"You're pulling my leg.",就变成某某人在愚弄你,你在发火,或者某某人真的正在拉你的腿.我要答案！！~~同义句的话应该是You are kidding me !You are joking me !（楼下有提到的）