It was, perhaps, the frustration and anger and grief that he still hadn't been able to deal with talking--it wasn't fair to dump this on Ezri, because it's not her fault, but hearing her say in not so many words that she wasn't good enough hit all of his anger points.

"So what you're saying is that you're not good enough," he says, voice twisting as the mask drops further, if only for a moment, his anger at the concept blatantly obvious. If she knows him half as well as she thinks she does, she should know exactly how significant those words are to him. Significant and hated. "Which is a load of shite, otherwise you wouldn't be here at all."