What's Mallard raving about today?
Father's Day, Cards.
I think Mallard's attempting honest sentimentality.
Unfortunately, the only facial expression he knows how to draw (or, rather, the only emotion we've ever attached to the one facial expression he knows how to draw) is smug disdain and superiority. So, it looks like that guy is mocking his son.
At that level (being an asshole), it fits in with the rest of the Mallard Fillmore oeuvre.
That said...Father's Day was yesterday you fucking moron.