Do not plant seeds of hatred in your heart. 

Soon, it will grow into small sprouts of envy. You will hate every single detail about that person even if there is nothing wrong about them. In your eyes, they are full of flaws. You will always say that there is something wrong about them but the truth is you are nothing but a fault-finder human being. And you hate them because you are jealous of them. You will never appreciate anyone. You will never see their worth because you are blinded by the hate you are feeling towards them.

These small sprouts will grow into a bigger plant of insensibility. Because of anger, you might by pass their feeling. You may never hurt them by means of physical actions, but you may use your words against them. Remember that words are like daggers. When you use them against people, they could be killed emotionally by those words. You could bring them extreme pain and they may bleed a lot inside. But the thing is, your insensibility towards their feeling might turn into apathy. And I believe not caring at all is even worse.  

Lastly, when you let it grow into a big tree of anger, you will found yourself underneath it and you will then be consumed by the darkness of its shade. So before it grows into an enormous tree, put a stop to it.