Some people have unresolved issues that come to the fore and are blinded by hate as a result of something that ticks it off. Yhat is the easiest way to face the aggravation, even when they would otherwise have acted more calmly had they reasoned there was no rational foundation to the hate in the first place.
So you could have a friend who will hate you because you were tired company one day, when he fails to see how he had his tiresome days too. It was easier to hate you for not being more lively. That was the reason for cutting off a fine friendship but then one may argue that the friendship was never there in the first place for such an absurd reason. This so called friend must have either harbored a resentment for not wanting to see himself or could not express his frustration in a more positive way.
Hate can be a nasty collection of acquired thoughts from others bent on disturbing your own peace of mind. We are generally aware of people who would love you to commiserate with them over a foul deal that affected their good spirits. Pleanty of people fail to see both sides of an issue and when it comes to sentencing a suspected convict, will go on hearsay rather than fact or will be so absorbed in their own hate that the person would be considered guilty no matter what his deeds were.
Hate comes from spoiled love, when a person feels transgressed. Often enough if the love was shallow there should be no reason for a pronounced hatred. One might just as well give up the relationship and carry on without dwelling on the scornful issues. In other words I question why people put so much energy to dislike someone when there really was no true sentiment of attachment. If you realize that the lover was hardly there for you in times of trouble, that would be one reason for you to love that person less. One could avoid the nasty sensation of wanting to avoid that person or not wanting to talk him by accepting the new reality. This does not make the deeds right of course but forgiveness also helps to calm the spirits.
We are responsable for the way we feel even though we get inputs from so many that cause us turmoil. Better to be good to yourself and not harbor rancor or distrust, two elements that tag along with hate. You would be better off not to hold a chip on the shoulder for an event that happened years ago especially when that moment has long gone and the issues around it have been resolved. Distrust creates a disturbing atmosphere as people will find it uncomfortable to work with you when you cannot see the positive side to life.