Behaviour: I Want What I Want!
To help in these situations, I found that I had to restate an alternative, and walk away and observe from a safe distance. No more talking. No responding to his demands. No eye contact, even though I was keeping an eye on him. If I could, I worked with another student, or worked at something else. The hard part was keeping quiet and not responding to his baiting. "I want what I want and you can't stop me."
Eventually, he would come around, especially if he saw that he was getting nowhere with his demands, and I wasn't reacting. He was a child who got something out of the drama of an argument. On occasion, he did end up staying on the computer longer than he was supposed to. That was addressed on the next "reward" --he could have a different preferred activity, but not the thing that he "took" before.
Deep inside, I wanted him to do what I wanted in the time I wanted, but that was not really possible. If I engaged with him and argued back, he was controlling the situation. It took a long time for me to see this, but I got further with this approach. The win is that the situation did not escalate into a shouting match. What strategies have you tried?