How can you stop a person ruining your life?

Answer 1

If they don't know that they're ruining your life, talk to them about it and explain how you feel, honestly, politely and civilly. If they do however, try to avoid them and just ignore whatever they do or say about/to you, trying to show them that you don't care. If that is impossible, laugh at them scornfully and derisively whenever they do or say something hateful or annoying or provoking and think up a clever answer (if they've said something) or just make a nasty joke at their expense if they've done something. Remember, you might have to be cruel to them, really cruel to show them you're not to be messed with but the important thing to remember is don't go out for vengeance- you're not trying to ruin their lives- you're not them.

Answer

By removing them from your life. If someone is "ruining your life" then arrange your own life so as to minimize your contact with them. In other words, take charge of your own life. Once you have recognized the other person doesn't bring something positive into your life it's on you to prevent them from having any control over you.