Here's a classic one: Tage Danielsson's The emperors new clothes:

One boy in the audience shouts:
But she's not wearing any clothes!
Then he had to leave since he was under 18. <img src="/ubbthreads/images/graemlins/ROFL.gif" alt="" />

Übereil

Brain: an apparatus with which we think we think.

Ambrose Bierce