intense emotion, hatred even.
A good hypothesis here may be that the one feeling the hatred towards another is projecting his or her feelings or attributes onto that other person, maybe some guilt or over- aggressiveness; however the deepest truth here may be that the hurt and twisted angry feelings are small when viewed from the lens of self hatred now being projected onto our partners, loved one or friend.
Our impulse, like that of a child who has just been criticized about a small misdeed by a parent, is to become emotional, upset, angry, to take the superior position. So then we don't have to feel the regard of another, to 'protect' ourselves from feeling anything at all.
The truth is, you may not be as horrid as you think; maybe someone did do something upsetting--do you now hate me? I already feel awful disappointing you; rather than getting mad and criticizing me, can you tell me in a more positive way?