What's Wrong With YOU?

My son likes to ask me, "What's wrong, mom?"  Then I reply, "Nothing.  What's wrong with you?"  And then he says, "What's wrong with YOU?"  It goes on and on, as he starts laughing.  Today, though, when I asked, "What's wrong with you?" he replied, "I shared a cup."  Me:  "You shared a cup?"  Son:  "Yes."  Me:  "Who did you share a cup with?"  Son:  "Big Brother"  Me:  "You shared a cup with your big brother?"  Son:  "Yes."  Me:  "And that's what's wrong with you?"  Son:  "Yes."  TOO FUNNY!