Both verbal irony and situational irony are identifiable in O. Henry's short story "After Twenty Years." The situational irony is clear, as the twist at the end of the story reveals an unexpected turn of events for Bob; the discrepancy between what actually happened and what Bob expected to happen make a clear case for situational irony.
The verbal irony is more subtly placed, like when Bob says to the cop, "In New York a man doesn’t change much," without realizing that the cop is Jimmy. Clearly, in New York, a man can change a great deal, if Bob can't recognize Jimmy and if Jimmy's attachment to Bob has changed so much that Jimmy chooses to stay on the right side of the law when confronted with the choice. Another example of verbal irony can be found when the cop approaches Bob, pretending to be Jimmy, and says, "We’ll go to a place I know, and have a good long talk about old times." Little does Bob know that the place he knows is likely the precinct and the long talk about old times will not be a friendly one.