it’s a still December night—no traffic, no sirens, no obnoxious noise or light. Across the street, a string of colored Christmas lights wrapped around a porch railing glow beneath a blanket of thick snow.
These few lines thoroughly paint a picture in the reader's mind and describes the setting of where the story takes place.
Plastering on a smile
By using this phrase, it conveys that the professor does not enjoy being in the class to do his job. He is unenthusiastic about teaching and overall adds on to the fact that he is a dull person.
Against the far wall a young man in sweat pants and a Minnesota Twins hat snores quietly—his desk empty, except for his head.
This statement adds imagery and indicates that his students are uninterested in being in his class, for he is always late.
He slings his bag onto the table up front and checks his watch—he’s five minutes late, as usual.
This sentence adds on to the previous sentence by characterizing his as also being careless and lazy. The word "slings" as well as the professor being "five minutes late, as usual" builds upon this characterization.
He strolls into his classroom wearing his uniform—faded black jeans that sag in the rear and a worn fleece pullover.
This sentence provides a vivid image in the reader's head of what he is wearing. By describing what he is wearing, the author conveys what this character is like. The words "stroll," "faded," "sag," and "worn" have a similar tone that characterize the professor as being bland, mundane, and dull.