I know it sounds odd, but would very much go in for 'kill it with kindness'.(Not literally of course) So in your examples, on refusing to answer the register, look up straight at the boy and say something on the lines of "Good morning xxx, I see you're here today but don't feel like answering at the moment. That's fine I'll mark you in." No further comment, though the boy might well then reply. If something rude, try to ignore or say quite calmly, "I understand you're angry/upset, but please don't use language like that/speak to me like that in my classroom." Ditto with dinner register. Pro-actively look for any opportunity to praise any co-operation/on task behaviour. If he's had a good lesson, praise him at the end as he leaves and say you would like to see more of the same. Have a place set aside for him to retreat to when troubled and take time to have a quiet word and reassure him you want to make the best of the situation.