If revenge is a dish best served cold, which is to say dispassionately, then irony is a dish best served with a secreted body part of a bug or small rodent, which is to say with a hidden agenda. Revenge is a dramatic way of getting one's own returned, a score settled, a slate wiped clean as in Poe's "A Cask of Amontillado" and Thurber's artful follow-up, "The Catbird Seat." Irony is the reader being allowed to eavesdrop on the difference between what is said and what is actually meant, as in Ishiguro's The Remains of the Day.
As an actor learns the essentials of the acting craft, it becomes increasingly clear that persons in real life and, consequently characters in drama, do not always say what they mean, covering intent with distracting gestures, contrivances, and disguises. As a writer learns the essentials of dialogue, it becomes increasingly clear that what passes for conversation must be driven by the inflections and attitudes of constrain, perhaps even caution, lest a misstep will let the genie out of the bottle.
Living with irony as a fact of the human condition allows the writer to impart complexity and dimension to a story, a complexity and dimension that extend beyond the alleyways and culs de sac of plot. To arrive at the point of living with irony, the writer profits from beginning each new scene with an investigation of the intent each character comes on stage carrying. Sometimes the intent is to keep status quo, to refrain from giving in to the smoldering resentment or impatience felt toward another character. If she says THAT one more time, I will scream. Of course she, whoever she might be, comes cheerfully into the scene, proclaiming THAT at the top of her voice. Thus are moments of tension formed, and even more thusly, another step is taken toward the goal of combustion. Now we are in a position where we do not actually have to see the "I" scream--we can end the scene shortly before the actual scream which, however skilled and excellent our descriptive powers may be, we could not do justice to the scream within the reader's mind.
No question about where to begin the next scene. Another character is remonstrating with "I." "I think it was terrible the way you shouted at her." Of course, you could have the remonstration take these lines, "I was really surprised that you were able to show such restraint."
We could also have a completely different set of circumstances:
"What's wrong? I thought this was something you really wanted to do."
"I do," she said, "but--"
"I've never made love with a sixty-year-old man before."
"If it makes you feel more comfortable," he said, "neither have I."