Su and Mr. Ho (Situational Irony)
Su works as a secretary for Mr. Ho, so she is in charge of organizing his personal and professional calendars. The irony of Su helping Mr. Ho juggle dates with his wife and his mistress and covering for him on the phone, and purchasing presents for both women on his behalf, is that she is being cheated on by her own husband. She even enlists her husband in purchasing gifts for Mr. Ho's wife and mistress, i.e. the handbags from Japan, and she and her husband laugh about how he'll get both women the same color bag. However, after Su learns of her husband's infidelity, helping Mr. Ho with his own becomes visibly more exhausting for her.
Mrs. Suen's Lecture (Situational Irony)
Mrs. Suen notices that Su has been spending a lot of time out of the apartment, getting home late, and generally not engaging with the other women who live in the house. This is after Su and Chow start working on their martial arts serial in Chow's second apartment that he rented for them to have privacy. Suen tells Su that it's alright to enjoy herself while she's young, but warns her against "overdoing it." Suen's tone strongly suggests that she and the other neighbors suspect that Su is doing something wrong or engaging in untoward behavior outside of her marriage. She suggests that Su makes sure her husband doesn't travel so much in the future. The irony here is that Su's husband is the one cheating, and that Su's morals are so rigid that she refuses to leave him or be unfaithful to him, even though she knows she would be happier outside of the marriage. The irony is also dramatic in the sense that the audience knows that Su's husband is the unfaithful one, but Mrs. Suen has no idea.
Mr. Ho's Judgement of Su (Situational Irony)
Similar to Mrs. Suen's judgement of Su, the puzzled look Mr. Ho gives Su when he tells her that a man named Chow called the office for her is doubly ironic given that Su facilitates his own extramarital affairs. One might think that Mr. Ho would not find it odd, given his own arrangements with his wife and mistress, that Su had male friends or companions outside of her marriage, but his look of judgement and puzzlement just confirms the gendered double-standard enforced by his generation. Further enriching the irony, his judgment is based on a false assumption about the nature of Su's relationship with Chow.
Chow's Return to Hong Kong (Dramatic Irony)
When Chow returns to Hong Kong and visits the Koos' old apartment, he asks about the tenants in Mrs. Suen's place. What he doesn't know is that Su came looking for him earlier that year, and Su has no idea that Chow is looking in on her when he visits his old place. Neither Su nor Chow realizes that the other person is so close, and so interested, in what they're doing. But the audience knows that they just missed each other, making the situation one of dramatic irony.
