Fiberbabe observes on the link on irony Jackie provided:

Some time ago, a Harvard English professor (or someone of similar stature who seems to get paid for doing these sorts of things) put together a treatise about how, technically, none of the citations in that song illustrated irony at all. The pithy & brilliant comment that I took away from it was "None of those qualify as irony - the best that any of them can be described is a bummer."

Go Harvard.

...wish we had a link to this prof's arguments. If you observed a person taking a cigarette break under a "No Smoking" sign, unbeknownst to the smoker, wouldn't that be ironic?

WW