Originally Posted by wetduck
Irony implies a group in the know, and a group not in the know.
That's one definition of irony. There are, of course, others. The generally accepted definition (of the sort of irony we are presumably talking about) simply requires that meaning be expressed by the use of different, usually opposite, language.
Sarcasm does not rely on these two separate audiences. Anyone reading your post would be able to tell that you did not mean at all what you said, and were merely mocking my post about irony. No second group that is clueless and therefore no irony.
You are certainly correct in pegging my response to your post as sarcastic. In this, your English degree has not let you down. You go astray only when you assume that your preferred definition of irony is the universal or authoritative one.