Talking badly about one person to another person can be defaming their character, also called defamation of character. If a person says something about another person that is not true, whether it be verbally or in print, or harms that person it is against the law and action can be taken against the person who committed the defamation.
Character or Standing
Most of the time it falls on the plaintiff to prove that a defendant defamed their character, but there are instances where the defendant must prove that the statements he made were based on facts. Making derogatory statements about a person's work or profession is an example of defamation of character. Hurting a person's position in a company in a way that harms her or hurts her reputation professionally is defamation of character.
Sexually Transmitted Diseases
A person who tells a third party that someone has a sexually transmitted disease is a form of defamation of character. This must be done to intentionally harm that person. Telling others that another human being has a disease that will harm others is hurting that person in the community in more ways than can be explained. This is generally called mental anguish and is a form of harm that deals with a person's mental state.
A person who publishes or communicates to a third party about the unlawful sexual acts of another person has committed a form of defamation of character. A person cannot say a wife or husband is cheating on the other without proof of that adultery. This claim can damage a person's marriage or relationship to others. If a person says that another person not married is having sex with children or animals, this is also defamation of character. It is indecent to make statements such as these.
A person who accuses someone of a crime of moral turpitude to a third party has committed defamation of character against the accused person if it is untrue. Moral turpitude is an evil act that is considered a crime. Crimes of moral turpitude include murder and manslaughter.