I know, I know, this is way easier said than done but you still need to emotionally take a step back. If you don’t, you’re likely to erupt in anger or sadness, which will stop you from doing anything constructive.
So your friend has told you that so-and-so (let’s name this person X) has said something bad about you. Are you sure you’re being told the truth? Maybe your friend has her/his own reasons for telling you a lie about X.
The best thing would be to talk to the person who spread the rumor and ask them why. Most will try and give an excuse (“Maybe he/she misunderstood what I said”/“I thought that’s what you meant”); you can ask X to stop spreading lies directly. If a friend can be there during the talk, great – because you have a back-up to your side of the story.
Maybe you can’t talk to X; maybe X moved and the gossip was a parting gift, maybe you know talking to X is useless, whatever the cause, that’s a dead end. You can still tell some people, who’re involved in the situation, the true version of things.
It may feel natural to want to lash out at others and talk bad about them in return. Don’t, because it will make you look bad as well. You can try to understand and explain why they did what they did (“Under pressure nowadays”/”Was scared of losing job”) but keep it clean.
Despite your best efforts some people will choose to believe the lies. That’s okay. When people feel bad about themselves, they like to believe others are bad too. Realize that for them this gossip is merely a wish to pull you down to their level.
Maybe what’s being said about you can seriously harm your career or life. Try and get some evidence of the lies and take it up with an HR person or even a lawyer if you feel threatened in any way. For this you will need proof so stay calm and think of how you can get it.
Not only because your friends or family members might have good solutions but if you keep fighting alone, you’ll feel tired and even more targeted. If people are staring, nudging each other or making comments, call a friend and just talk to them.
You know you didn’t do whatever it is you’re accused of, so don’t suddenly start behaving out of character otherwise people have more reason to believe it. If you are a truly likable and good person, then those with sense will realize that what they heard can’t be true.
Unfortunately, some poisonous people are very good at character assassination. Maybe, despite your best efforts, you can’t get people to see your side or even leave you alone. Get away from such a situation because it can affect your mental and physical health.
Being targeted by malicious people can make the cheeriest person feel low; you felt bad about it too. When, however, you move on with life, don’t indulge in gossip or rumor-mongering about others. There’s no happily-ever-after for hateful people.