Ephesians 4:31-32 says: "Get rid of all bitterness, rage, anger, harsh words, and slander, as well as all types of evil behavior. Instead, be kind to each other, tenderhearted, forgiving one another, just as God through Christ has forgiven you."
This verse means exactly what it says.
Why would you want to have bitterness inside of you?
Why would you want to have rage and anger inside of you?
Why would you want to say harsh words to someone, and use slander?
Those things won't make us feel good, even if we think it will.
Instead, be kind and tenderhearted. Forgive one another for what they do, instead of holding a grudge. Do this, just as God through Christ has forgiven you.
He did this for you, so why can't you do that for him?