This is an accessible and very commonly used form of irony in everyday speech. You may have heard some examples of verbal irony without even realizing it. Verbal irony usually occurs when a speaker says the opposite of what he actually means. It can also occur when, as a result of prior knowledge, an audience realizes that the opposite of what a speaker says is true. An example of verbal irony would be someone saying, "Great," when things are actually going horribly. Timing and delivery are critical elements in being able to convey this kind of irony.
Situational irony, or irony of outcome, is typically seen in literature or drama. This kind of irony can be positive or negative, tragic or comic, but it is a term used to highlight the unfairness or strangeness in a certain situation. Despite its versatility, situational irony can be most powerful when it occurs in a tragic situation because it highlights the fragility of life, especially in terms of material possessions. For instance, in "The Gift of the Magi," the two main characters secretly sell their most prized possessions to purchase Christmas gifts for each other; the irony is that the gifts correspond to the items that were sold and are thus useless.
This kind of irony is used when people or characters feign a lack of knowledge on a certain subject when they are actually quite well informed. Socratic irony gets its name from Socrates, who originally employed this tactic to provoke audiences and spark debates in a peaceful manner. Today it is used in classrooms when professors feign ignorance on certain subjects to promote original thoughts from students. It can also be used to gain an advantage in a debate or argument or to avoid talking about an unpleasant or uncomfortable topic. For instance, if a child asks his parents how all the Christmas presents got under the tree, the parents might say "We have no idea how those got there!"
Dramatic irony is seen in works of literature or drama when a character is about to make an error because he is unaware of a fact that the audience already knows. A subcategory of dramatic irony is called tragic irony, and it gets its name from the tragic consequences that it causes. "Romeo and Juliet" offers an example of tragic irony; the audience knows that Juliet is not really dead as Romeo prepares to take his own life. This kind of irony produces heightened suspense because of the audience's inability to aid the character in trouble.