Found this on another discussion board in a topic about the difference between irony and sarcasm, thought it was good enough to share:
"Irony" refers to a state of affairs, not a use of words. It refers to a result that is the opposite to, and mockery of, the appropriate result.
For example, if Rush Limbaugh is struck and killed by a runaway car, that is an accident.
If Limbaugh is struck and killed by Randi Rhodes' runaway car, that is a coincidence.
If Limbaugh is struck and killed by Sean Hannity's runaway car, that is a bit of an irony.
If Limbaugh is struck and killed by the runaway car of the lawyer who kept him from going to jail because of his illegal drug use, that is a bigger irony.
If Limbaugh is beaten to death by the doctor who, all those decades ago, very probably saved Limbaugh's life by keeping him from going to Vietnam due to a zit on his ass, that's a BIG irony.
If after this happens I remark, "Good thing he got the military training in Vietnam that saved his life from that brutal assault," that is sarcasm.