The stubborn part of Thor stiffens the moment that Tony says that he's likely going to get angry. Not in preparation for getting angry, but in preparation for not.

But true to Tony's word, Thor finds himself bristling with irritation at Tony's ask.

"I don't think that's something you get to decide." Thor grabs a marshmallow and stares out at the tent because he doesn't particularly feel inclined to look Tony in the face right now.