To be ironic means to speak in contrast to what you really mean. Usually, people are expected to pick up on it by tone of voice.
Irony is what most people think is called sarcasm. It is a form of intentional wordplay, derived from the behavior of the Eiron, a feature of greek theater. (Sarcasm is irony which is meant to hurt feelings.)
Irony is not what Nelson from The Simpsons would laugh at, and is never unintentional.
If a safety worker botches the installation of a safety device which later gets them killed, that is not irony. When someone leans over the rail and yells "good job keeping people safe," that is irony (and since it's mean, it's also sarcasm.)
Irony is what most people think is called sarcasm. It is a form of intentional wordplay, derived from the behavior of the Eiron, a feature of greek theater. (Sarcasm is irony which is meant to hurt feelings.)
Irony is not what Nelson from The Simpsons would laugh at, and is never unintentional.
If a safety worker botches the installation of a safety device which later gets them killed, that is not irony. When someone leans over the rail and yells "good job keeping people safe," that is irony (and since it's mean, it's also sarcasm.)
http://rhetoric.byu.edu/figures/i/irony.htm