This type of irony is popular in works of art such as movies, books, poems and plays.

It occurs when the audience is aware of something that the characters in the story are not aware of.

An example of dramatic irony is in a movie where a detective does not know that the criminal responsible for the crimes in the city is his partner. The audience however is already aware of this fact and waits anxiously to know what will happen once the character finds out what they already know

Situational Irony

It involves a discrepancy between what is expected to happen and what actually happens.

Situational irony occurs when the exact opposite of what is meant to happen, happens.
An example would be when someone buys a gun to protect himself, but the same gun is used by another individual to injure him. One would expect that the gun would keep him safe, but it has actually caused him injury.

There is however a difference between situational irony and coincidence or bad luck.

When someone washes his car and it rains, that is just bad luck; nothing led him or her to think that it would not rain. However, when a TV weather presenter gets caught in an unexpected storm, it is ironic because he or she is expected to know the exact weather changes.

For situational irony to occur there has to be something that leads a person to think that a particular event or situation is unlikely happen