Scared of teacher, but bully mommie?!

This morning during our cab ride, I brought along a little book for Shawn. He was more distracted by the aerochamber box in his bag (for ventolin puff). I said, "No, Shawn. You are not supposed to take that." He whined and whined and whined. Then he tried again and I said the same thing. Then he whined and tried to take the box again. Then I resorted to say this, "No, this box belong to teacher. You are not supposed to take okay?" He kind of quiten down a bit. Then minutes later he tried again. And I said that belongs to the teacher. Then he decided not to pursue anymore. It worked at least for this morning. Perhaps I would try to the same trick if he tries anything funny again.