Joss felt nervous because meeting the parents was always a scary thing to do. And he wasn't strictly human so he had to make sure he said the right things. These weren't just Maddy's parents to him, they were also his nephew's grandparents and he wanted them to like him.
He was dressed casually when he arrived at Maddy's and he grinned widely at her when she opened the door for him. "Hello!" he said excitedly.