Theodore almost wished he would attack, to give him a legitimate reason for teaching him a lesson, something that he'd been very strongly resisting so far. But he started closing the door as soon as Borgin finished I'll be back, and cut him off just before he'd finished, with a satisfying click of the locks and wards settling into place again. He didn't even bother to respond.
He went back up the stairs to Tracey, attempting to shake off the cold, unemotional expression on his face before he got to her, but didn't quite succeed. "I'm sorry about that," he said, looking at her. That, at least, made his expression soften and warm up. "I shouldn't have opened the door."