Old Testament
Even a Fool, when he holdeth his peace, is counted wise.

Shakespeare
The Fool doth think he is wise, but the wise man knows himself to be a Fool.

Cowper
A Fool must now and then be right by chance.

Proverbs
Answer a Fool according to his folly.

Tusser
A Fool and his money are soon parted.

Plato
Wise men speak because they have something to say; a Fool because he wants to say something.

Aeschylus
A prosperous Fool is a grievous burden.

Cicero
Any man is liable to err, only a Fool persists in error.

Messageboardfools.com
Hey!... you're really stupid.