Bobby knew he irritated the team with his "class clown" attitude. But he did it to deal with the world. He could become a living ice sculpture, but that didn't mean he was cold hearted. The insults people threw at him hurt, so he joked around to deal with it.
He had ice in his veins, like John had fire. He wouldn't understand what it felt like to be 'hot-blooded,' but he could understand how it was to be set apart from others, even among mutants. It was hard, but he would deal with it, just like he usually did.