It is ironic when Della sells her hair to buy Jim a gift for his watch, but he can’t use the gift because he sold his watch.
Situational irony occurs in a story when the opposite of what you expect to happens is what happens. In this story, both Della and Jim’s gifts are ironic. Since the story follows Della’s point of view first, hers is a good example.
Della feels inadequate because the couple is poor and she has barely scraped together enough for a Christmas present. She wants to do something nice for her husband, because she loves him. She decides to make the ultimate sacrifice and sells her hair to get money to buy him a watch band for his most prized possession.
It was a platinum fob chain simple and chaste in design, properly proclaiming its value by substance alone and not bymeretricious ornamentation—as all good things should do. It was even worthy of The Watch. As soon as she saw it she knew that it must be Jim's.
At this point, we would expect Jim to come home and be thrilled at the gift. After all, he loves his watch and the gift shows how much Della cares. She sacrificed her beauty and her pride to get him the watch band. The situation gets ironic when Della sees Jim’s unexpected reaction to her cutting her hair. She thinks he is angry.
It was not anger, nor surprise, nor disapproval, nor horror, nor any of the sentiments that she had been prepared for. He simply stared at her fixedly with that peculiar expression on his face.
It turns out, Jim is just stunned. He sold his watch to get her the gift of her dreams, or so he thought. He bought her combs for her long, beautiful hair. He is baffled by her haircut because he realizes the stunning irony before she does. They each sold what seemed to be most important to them, thus proving that what is most important to each one is the other one.
The beauty of this story is in the situational irony. The reader realizes that the two silly young lovers are actually very wise. They each gave up a superficial possession in order to show their love. In doing so, even though neither could use the gift, they each gave the other the best gift of all. They proved their love. This is why they are called the magi.