What is the irony of "The Catbird Seat"?What is considered to be dramatic, verbal, and situational irony?

Erwin Martin manages to turn the tables on his nemesis in James Thurber's short story, "The Catbird Seat." Martin appears to have little chance of maintaining the status quo at F&S once Ulgine Barrows becomes employed. As the new special advisor to the company president, Mr. Fitweiler, Ms. Barrows has gained the confidence of her boss and the changes that are being made throughout the firm appear to be headed Martin's way. Although he has no definite plan, Martin goes to see Barrows at her home with the intention of killing her. He does not even take a weapon along, looking around her apartment for something that will put an end to her along with his own misery.

But, as he puffs on a Camel cigarette that he has purchased,

Somewhere in the back of his mind, a vague idea stirred, sprouted... The idea began to bloom, strange and wonderful.

Martin realizes that no one could ever believe that he would show up in Ulgine's apartment, much less while smoking a cigarette. He was a creature of habit, of routine. So, Martin begins the transformation that he knows no one will accept. He berates Fitweiler, promises to kill him with a homemade bomb, and admits that he will be "coked to the gills" when he does it. He then warns Ulgine to keep quiet, knowing that she will report the incident to Fitweiler first thing the next morning. When she does, the president assumes that the pressure of her job has gotten to her and orders her away.

Martin has reversed the situation and assumed the catbird seat himself on which Ulgine Barrows seemed so secure. It is the supreme irony of the story.