“A fool vents all his feelings,
but a wise man holds them back.”
Proverbs 29:11

You oftentimes can tell a fool in the crowd – he or she is the one doing the most talking.

When you’re in a discussion with such a one, ask yourself,
. Where is this going?
. What is my purpose in continuing this?

If there’s no foreseeable point, stop right there, and change the subject. He’ll be
totally unaware of what you just did.

In order to do that you have to be aware enough to not answer from anger. When one answers in anger, he descends to the same level as the fool.

“…for the wrath of man does not
produce the righteousness of God.”   
James 1:20

Instead, take the high ground. Leave the fool in his foolishness and walk away. That will take some exercise in self-control on your part, and the first step is being able to view a foolish discussion for what it is.