Is it a sin to say mean things about someone if no one hears it?
Here's the answer:
God doesn't want us to say mean things, even if no one hears us.
We all get angry sometimes, and we all want to say mean things or have mean thoughts about others from time to time. It's natural to feel angry at a bully who hurts you or an annoying sibling or at a bad situation with a friend. Feeling angry about those things is not a sin.
The Bible is clear that we should not be gossipers (Proverbs 20:19). Gossip can be very hurtful and can harm friendships (Proverbs 16:28). But what if no one is listening? Is it still sinful to think about others' faults and mistakes and how we've been hurt by them? Thinking over and over about how mad we are only leads bitterness and sadness, which only leads to more hurt.
Bring your feelings and concerns to God in prayer. God knows every person's heart, so He will not judge you or the other person based on what you've said about them. Talking to God will help you let go of your anger toward another person too. Even King David prayed to God about the people who hurt him. We should not allow ourselves to stay angry for long and let it bring us down. Dealing with anger responsibly and healthily is a part of being like Jesus Christ.
"…'When you are angry, do not sin.' Do not let the sun go down while you are angry" (Ephesians 4:26).
"Instead, we will speak the truth in love. So we will grow up in every way to become the body of Christ. Christ is the head of the body" (Ephesians 4:15).
"Get rid of all hard feelings, anger and rage. Stop all fighting and lying. Don’t have anything to do with any kind of hatred. Be kind and tender to one another. Forgive one another, just as God forgave you because of what Christ has done" (Ephesians 4:31-32).