What are a few ironic points made in the story?
Irony exists on several levels. On the linguistic level, the fact that "the man" of the title calls Jensen "boy," reversing a standard linguistic practice of whites towards Blacks, is ironic.
On the level of physical action, the man puts his hands around Jensen's neck, in a gesture that Jensen finds threatening, but he does so just to measure Jensen for shirt size for a gift. To threaten while giving is ironic.
On the level of plot, the fact that Jensen warns Lena about the man, only to have them get married, is ironic.