Seven year-old monster of a son...?

I think he is angry with you, maybe even holding a grudge for always being in trouble. Of course it is his own fault but he might feel like you love the younger brother more. Like you say he's hardly ever rewarded unlike the other one and he sees this as unfair treatment. I think he needs more positive attention. He just needs a taste of it so he'll try for it a lot more. Even the littlest things like putting his bath towel in the hamper, take notice when he does a good job and tell him "Thank you".