Benjamin Falling in Love with Elaine (Situational Irony)
After becoming caught in the catch-22 between Mrs. Robinson's forbidding him to date Elaine and his parents' urging him to ask her out, Benjamin initially tries to sabotage any connection he might have with Elaine. Fearing the wrath of Mrs. Robinson, Benjamin drives recklessly, takes Elaine to a strip club, and behaves brusquely with her, hoping that he can get the date over with, without any negative consequences. Ironically enough, he ends up falling for Elaine, and disregarding Mrs. Robinson's threats. Benjamin abruptly kisses Elaine outside the strip club, and as they get to know each other over dinner at the drive-in, it becomes increasingly clear that he feels a genuine and unprecedented romantic connection with her. Elaine is the one person with whom it would be unwise for Benjamin to fall in love, given that he had an affair with her jealous and vengeful mother, but inconveniently enough, they are perfect for each other. While Benjamin intends for the date to go badly, it ends up being perhaps the best date of his life.
Mr. Robinson telling Ben to "sow a few wild oats" (Dramatic Irony)
Mr. Robinson's advice to Benjamin that he "sow a few wild oats" and experiment sexually before settling down is a moment of comical dramatic irony. Dramatic irony occurs when the viewer knows something a character in the film does not. While the viewer has just witnessed Mrs. Robinson's aggressive seduction of Benjamin, Mr. Robinson has no knowledge of it, and simply wants to encourage Benjamin "man-to-man" to experiment sexually in his youth. The fact that Mr. Robinson's encouragement comes directly on the heels of his own wife's sexual propositioning of Benjamin creates a particularly humorous and tense irony. To the viewer, it seems as though Mr. Robinson is encouraging Ben to have an affair with his wife, but of course he has no idea that this is even a possibility.
Elaine's Belief in Mrs. Robinson's Accusation of Rape (Dramatic Irony)
Another moment of dramatic irony occurs when Elaine believes her mother's accusation that Benjamin raped her. The viewer knows that Benjamin did nothing of the sort, and that it was in fact Mrs. Robinson who was the sexual aggressor in the affair. Thus it becomes ironic that Elaine accuses Benjamin of having initiated the affair non-consensually, because the viewer knows the affair to have begun mutually, and at the urging of Mrs. Robinson. There is a discrepancy between the perception of Ben as a rapist, and the viewer's knowledge that the person accusing Benjamin of rape is the person who initiated the affair.
Ben's pressuring Ben to ask Elaine out (Dramatic Irony)
Immediately after Mrs. Robinson makes it clear that she forbids Ben from asking Elaine out on a date, Mr. Robinson and Benjamin's parents conspire to get him to do just that. Benjamin's parents are in the dark about his affair with Mrs. Robinson and her threats about his interest in Elaine. Benjamin is of course prevented from telling them, for fear of their judgmental response, and so they are left in the dark. While the viewer understands the full complication of the situation, Benjamin's parents forcefully urge him to ask out Elaine, even threatening to invite the whole Robinson family over if he doesn't. The audience knows that a date with Elaine will only make matters worse, but the Braddock's naively coerce him into doing so. Benjamin is trapped in a catch-22, to which only the viewer is privy.
