Denying God's existence is foolish. It's in the Bible, Psalm 14:1, NIV. "The fool says in his heart, 'There is no God.'"
The things of God seem foolish to the unbeliever. It's in the Bible, I Corinthians 2:14, NIV. "The man without the Spirit does not accept the things that come from the Spirit of God, for they are foolishness to him, and he cannot understand them, because they are spiritually discerned."
A fool has no self-control. It's in the Bible, Proverbs 29:11, NIV. "A fool gives full bent to his anger, but a wise man keeps himself under control."
Fools talk too much. It's in the Bible, Proverbs 10:8, NIV. "The wise in heart accept commands, but a chattering fool comes to ruin." Proverbs 17:28, NIV. "Even a fool is thought wise if he keeps silent, and discerning if he holds his tongue."