3 forms of Irony
Verbal Irony: The use of sarcasm. Someone says one thing with the intention of that statement meaning something very different. A person says to another, “you look so beautiful,” with the intention of meaning, “you look awful.” The purpose of verbal irony is to say something, yet mean something completely opposite.
Situational Irony: The outcome of events or action someone takes is incongruent with what was expected to happen versus what actually did happen.
Dramatice Irony: The audience is aware of a thought, intention, action or event that the character is unaware of.
You can visit this site for further explanations and examples: http://theoatmeal.com/comics/irony