What was the idea with the man with glasses and hat on the subway?

There's a man with glasses and a hat who stares quite pointedly at Llewyn on two different occasions while he's riding the subway--the first time (at 9 min into the film) when Llewyn's got the cat with him and the subway is crowded, and the second time (at 42 min into the film) when there's no one besides them in the subway car.

On the second of the two occasions, Llewyn notices this man's stare and glares back at him.

Did this make sense to anybody?

The man is a rather striking-looking figure (he's not just some typical suit-and-tie type) and these interactions are really the only ones in the movie between Llewyn and any random individuals out in public--which is why I wonder about them.