One's first thought in reading the title would be that the speaker is up to some nefarious purpose, pursuing nightime activities that could not bear the light of day. It seems sneaky, and even evil. Yet in reading the poem, we see that the speaker is acquainted with night as an observer. Yes, he sees the sadness and the crime, but he is not part of it. His acquaintance is only from a distance, not by direct participation. Therefore, the irony lies in the reader's expectation of a sinister narrator, when in fact he is a neutral observer, thus causing the reader to question exactly the level of this "acquaintance."