It's really not that hard of a concept to not talk negatively about other people, yet people still do it. I get it, you're bored and it's easier to tear other people apart rather than fix yourself. It's the easy way out but stop it.
There is absolutely no point or need to disrespect a person like that. I don't care what the person has said or done to you, there is no need. Accept it, forgive and move on. Keeping hate in your heart will only hurt yourself at the end of the day.
What's the point? To feel better about yourself? There are other ways to feel good about yourself. Maybe you could get into a club you like, sports, music, etc. If you need to rip others apart at the seams to feel superior than you have a serious problem.
Is it a person who broke your heart? Or an old friend that left you out of the blue? Someone who stoped talking to you to better themselves? Get over it. This may seem like tough love but you can never truly get over someone or a situation if you don't keep talking about it. Take your time to mourn and then move on past it. Stop obsessing over the past and what you can't change and move on. Grow up and stop talking negatively about everyone because it's not going to get you anywhere.