On January 21, 2000, Reuters reported that Justin Kruger and David Dunning had released the results of a study that answered a question many of us have asked ourselves: do the incompetent (or conceptually retarded) realize that they are?
They found that people who are ignorant in a given area (they tested things like logic, grammar, and sense of humor!) tended to over-rate their abilities, while people who actually had some competency or knowledge in the field of inquiry tended to much more accurately assess their skill level. In other words, "Incompetents lack the basic skills to evaluate their performance realistically."
So the next time you wonder, "Does that guy really think he's funny?"...

Pity him. He doesn't know.

Or envy the unselfconcious. And hope your ego doesn't deceive you.