Proverbs 14:17

A man of quick temper acts foolishly,
and a man of evil devices is hated.

This proverb points out the danger that comes with anger: we make fools of ourselves. More times than not, we regret our words spoken and actions committed in anger. We harm people we love; we lose or destroy possessions valuable to us. Anger makes us dumb. All the more trouble then for a quick tempered person.
Such a person may be zealous to serve; he may be compassionate; in other respects he may exhibit godly character. But his temper continually destroys what his good character produces. People are guarded around him, unable to receive his attempts to befriend them. He cannot be entrusted with responsibility despite his giftedness. He is regarded as a danger. If you have this problem, take steps to receive counsel and accountability. There is nothing more destructive in your life than a quick temper. Make it your daily prayer for healing.

A man may mean well but be distrusted for his quick temper. A man of evil devices is hated, for his very intent is to harm his neighbor. He devises ways to take advantage of others for his own gain. He may be able to master his temper, but he does so in order to get his way. The joke on him is that he thinks he is clever but is really a greater fool. Unlike the quick tempered man, he keeps his cool and plans ways to manipulate his neighbor. But though he is able to fool others for awhile, his evil heart becomes known through the hurt he causes, and so he wins hatred. The rest of his life, he must keep devising schemes to offset the hatred he has earned and the attempts of others to harm him. He is a fool, thinking that losing the respect and love of his neighbors is worth winning the trinkets of money and power.