An ironic tone is an expression of a writer's attitude toward their subject, often conveyed using sarcasm, exaggeration or understatement. An ironic tone calls attention to the difference between the way a subject is described and what is actually true about that subject. Irony is often used for satirical writing, which commonly seeks to criticize its subject.
In fiction, an author can express an ironic tone through the use of diction, paradox, juxtaposition, character actions, plot or dialogue. An author's specific choice of language can create irony through the description of a character. A malicious character might be described as being gentle as a wolf, with the fundamental disparity in the description serving to create an ironic tone.
An ironic tone can also be created through dialogue choices. A wife who finds her husband boring and predicable might remark, "I just never know what you're going to say next." Because the reader knows that the opposite is true, the dialogue creates a tone of irony. Sarcasm is one of the more overt methods to create an ironic tone, but irony often depends on more subtle, understated language to make its point. The woman might instead simply remark, "Interesting." If the reader knows that the husband is boring, the tone of irony is clear, even if the wife's remark is less caustic.