It was hardly the first time he'd been mistaken for Severus, but it was one of the few times he'd been in the frame of mind to take advantage of it. He was feeling good and in the mood for a bit of fun, and so he schooled his features into a forbidding scowl like one of Severus'.
Given the young woman's age and how she had addressed him, he assumed she was one of Severus' former students, and it wasn't difficult to imagine how Severus would have acted under the circumstances.
"That is Mister Snape now," he snapped imperiously. "I retired three years ago, and I no longer have to waste my time trying to impart my wisdom and experience to mindless dunderheads."