Perhaps Severus is allowed to laugh, or affect amusement however he may. The look Lucius deals his way is sharp, as if searching for it, and he allows for his own halved if unhidden smirk, slightly dour but nevertheless there. It is what it is, and what it is is ridiculous. He dismisses Severus again, tipping attention back to his drink.

"You've an impressive imagination," is just as droll, reaching to collect the bottle to top up his own glass in careless splashes that never actually go beyond the glass's rim.

Set back down, closer to Severus if he wants it, before he takes up the glass again. "I suppose I ought be grateful that that's the only trace of fatherhood I've had to affect since being here." He doesn't sound like he is, but he doesn't sound like he isn't; it's almost an objective observation, stepping neatly around the sentiment of the matter, played for dry humour.