That gets a reaction - even slight - and Severus makes a bit of a face, just a near-delicate wrinkle of his nose, recoiling a little at it.

"You haven't." Flatly. He is no one's professor; yes, he's taught for a few years, but it's not a role that he identifies with in any way, and in fact rather resents it. (It bothers him, knowing it's something he could enjoy doing, but that such a fulfillment is barred from him.) The man next to him, meanwhile, is practically radiating awkwardness until Severus shoots him a look and he takes it as permission (or maybe an order) to flee to the back room.