Focus on that word, fool, for a moment. I can't tell you how many times I've heard people call others fools, intending to criticize but ultimately looking like fools themselves. What I mean by that is that when you poke fun at others because of the way they look, act, sound, etc., you're doing it because you really want to take the heat off of yourself. You want to elevate yourself into this "Look at me; I'm really wonderful and that person is NOT!" position. And the only way to do that is to put someone else down.
Here's what the Bible says about fools:
"But I tell you that anyone who is angry with his brother will be subject to judgment. Again, anyone who says to his brother, 'Raca,' is answerable to the Sanhedrin. But anyone who says, 'You fool!' will be in danger of the fire of hell." Matthew 5:22 (NIV)
"How long will you simple ones love your simple ways? How long will mockers delight in mockery and fools hate knowledge?" Proverbs 1:22 (NIV)
"As a dream comes when there are many cares, so the speech of a fool when there are many words." Ecclesiastes 5:3 (NIV)
"The wisdom of the prudent is to give thought to their ways, but the folly of fools is deception." Proverbs 14:8 (NIV)
There are tons more verses that speak of fools and foolishness, but you get the gist. Note: the reason I quote more from the NIV than other translations is simply because the Bible I use the most is a large one with bigger print (I have really bad eyesight) and it's an NIV. I also like the KJV and the NKJV.