why does derek hate to be called a 'poor boy'?

Derek hated being called a poor boy because he was not poor. In his opinion that kind of comment was a cover for what the person actually thought. To them, he seemed like a monstrosity and they were afraid of his face. Derek was also afraid of his face when he looked in the mirror. He had got acid all down on one side of his face and it burned away. It ate up his face and eventually devoured him too mentally.