"Dop yaf at me!"

Again with the whole, "I don't know where he gets these things" thing.  Matt, Henry, Evie and I were sitting in the living room the other evening, just talking and playing and spending a bit of family time together before bed time.  Matt told a funny story and we both started laughing when dear little Henry stopped what he was doing, got very indignant and yelled, "Dop yaf at me, Daddy!"  We both stopped laughing and looked at him for a second before I lost it completely.  Matt laughed a bit but composed himself very well and told him, "I'm not laughing at you, buddy."  Laughing, I assured him that I WAS laughing at him and he got soo mad!  He looked almost like he was going to cry before I started tickling him and got him to forget it.  But where would he have heard that?  Why does he know the concept of "laughing at someone"?  Doesn't he seem a little too young to know what that is?  It's crazy what a clever clogs that boy can be sometimes.  :)