" WHAT ARE YOU LAUGHING AT?"?

If a person in a high position is making a joke and then everyone laughs including you. You are not included in the convo but you are sitting one seat away from the person so the joke was in ear distance. What do you say when that person turns around, faces you and says "What are you laughing at?" in a serious manner. Put me in an awkward place. All I said was "Pardon?".