Confusion

I am confused about page 106, when one of the listeners to Marlow's story growls "Try to be civil, Marlow."

I don't understand why this is the first time one of the listeners really says something. Marlow has mentioned  dead people with bullets in their heads, but only after this passage he is asked to be civil. He points out his listeners "respective tight-ropes" and his own "monkey tricks," but this, it seems to me, shouldn't be as response-provoking as the rest of his story has been. Maybe it is because it attacks the actions of Marlow and his peers, while his whole story addresses the problems in the entire colonial enterprise. Maybe the listener doesn't care until Marlow's speech affects him directly.

Juicy Sentence

p.67 "And further west on the upper reaches the place of the monstrous town was still marked ominously on the sky, a brooding gloom in sunshine, a lurid glare under the stars."

I love paradoxes.

In this sentence, the narrator is talking about London. Previously in the passage, London had been mentioned as the greatest town on earth, but now it is filled with ominous paradoxes. The public image of London is generally not so negative. I know London is usually overcast and foggy, having the potential for gloom, but that is not what I think of. Maybe its because the weather was perfect and sunny for the two days I visited London, but when I think of London I think of rich history, glory, and royalty. All those generally have several negative effects, but not without the coverup of the cherished glamour of a major city. In this sentence, the narrator changes our view to help us find gloom underneath the supposed sunshine of a glamorous city. And so the paradoxes, "brooding gloom in sunshine" and "lurid glare under the star" make us second-guess our preconceived notions about the city of London. Furthermore, these paradoxes foretell that the following story will undercover a darkness in the Congo that contradicts the imperialists' coverup stories of humanitarianism.