There were plenty of things Zach could have said to argue with her, but at the moment he had no desire to do so. Tracey liked being right, just as much as he did, and no matter what he said, he knew he couldn't convince her it hadn't been interesting, amusing, or anything of the like.
Oh, but he wanted to tell her. The only thing stopping him was knowing she'd probably spill the dirt to everyone that he felt insecure.
"I'm surprised you came here of all places. There are plenty of other spots in Hogsmeade." He returned to his drink momentarily. "You should at least have some water or something. You're taking up space."