My sister lies about me a lot. what can I do?

slap her.

Actually, this is not legal but based on what types of lies she is spreading, you could probably send her a CEASE & DESIST letter asking her to stop spreading lies about you - especially ones that are causing your/your family's reputation to be harmed. Ask the people she is lying to about you if they will give a short affidavit stating the same - you may have a case for slander, which in some states actually falls under stalking laws. I know what you're going through because my sister did the same to me - said that my husband cheated, that I had bi-polar syndrome, et. When I had heard these things from five other people, I sent her the letter. I even volunteered to allow her to pick a psychiatrist of her choice to diagnosis my "bi-polar" problem and asked her to give details about my husband's alleged "affairs." I have no specific reason why she lies about me other than she has very low self-esteem and a huge inferiority complex. She not only lies about me but lies about and to everyone. My family believes she is addicted to lying - in essence, it makes her feel good for the second she tells it. The problem is that she forgets what lies she actually tells from day to day and on top of that, will deny she told the first lie. If you threaten her with the truth, she will cut you off and then proceed to get back at you with, lo and behold, more lies.