I know you are, but what am I?

This past weekend I went home to say hi to my family in far far away Metairie, LA and my cousin was in town with his 6 year old child. While I was playing around with him I called him a little booger, and then he said" I know you are, but what am I? I just agreed with him and went on playing. On monday we learned more about types of common falacies, I found the statement "I know you are, but what am I?" most related to tautology which is a type of circular argument that makes the statement impossible to disprove. It is understandable that a 6 year old would make an arguement like this, but later that day I was discussing what I learned in World Religions with my aunt and she disagreed with me on some facts. Instead of having a reasonable argument with me, she said,"I know I'm right" and stormed off. This proves to me that true arguments are difficult to have and common falacies are the easy way out.