An example I found that is meant to illustrate the difference between mere unfortunate happenstance and actual irony, is this one:
* **Accident/Conincidence:** If a diabetic, on his way to buy insulin, is killed by a runaway truck, he is the victim of an accident.
* **Poetic coincidence:** If the truck was delivering sugar, he is the victim of an oddly poetic coincidence.
* **Irony:** But if the truck was delivering insulin, ah! Then he is the victim of an irony.
As I understand it, irony is about opposites. So situational irony is about the opposition from what you’d expect occurring. How is the latter situation the opposite of what was expected to happen? It seems like it’s just something random and wildly different from what was expected, albeit with this undercurrent of dark, twisted humor.