Unfortunately, the Hulk doesn't have much room for a sense of humor right now, even Iron Man-- okay, maybe especially Iron Man's. He tenses when he feels the hand in his hair, half a growl escaping; that's a reflex, the reaction of an animal caught in a trap, but once he realizes Tony's comforting him, he relaxes. And then he takes his hand away and leans into Tony's touch, his eyes closing. That sigh is relieved.