Bitterness is anger gone sour, an attitude of deep discontent that poison our souls and destroy our peace (Billy Graham) . Let all bitterness, and wrath, and anger, and clamour, and evil speaking, be put away from you, with all malice:

And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you. Eph. 4:31-32