(Proverbs 26:24 KJV) He that hateth dissembleth with his lips, and layeth up deceit within him;
No one can know what is really going on in your heart. God does, but the person next to you can only deal with what they can see and hear. So the person you see may not be the person that is really there. A hater “lays” (7896) up all of the anger, animosity and desire for vengeance. He is constantly building a foundation of hostility in his heart.
Sooner or later it will bust out and be destructive. There is nothing you can do about it when it comes from someone else.
You can do something about it in your own life. You can review your heart and the feelings that are there. Look for fears, anxieties, dislikes, hostilities or anything else that might indicate you are not right with an individual or a group of people. If you are not sure you might want to share with a trusted friend. Then take it to the Lord and ask for forgiveness and healing.
So? If you just store it up, it can poison your personality, your daily life and your eternity. Hatred is destructive and sometimes subtle. Blessings on your journey.