[He goes from crying to hmmphing in an impressively rapid change of demeanor that only he is capable of.]

It is not my fault that you can't take a joke. Perhaps if you could hear over the volume of your own voice, you would notice that it was just joking.

[He's trying for a smile now, laughing softly (giggling) and reaching out to grab your wrist and pull you close.]

Hey, hey, come here. I have a secret just for you, okay? You can't tell anyone or I will smush you~