It's been said that nobody can make you feel bad about yourself without your permission. Well bah! Some people don't wait for your permission to denigrate you. They are toxic. Lifehacker.com offers some ways to deal with such people.
If someone's words have made you feel bad about yourself, then spend some time giving yourself pats on the back and positive labels. Make this a habit.
Empathy and Compassion
Towards the offender? Yes. Like Madonna says in her song, "Oh Father," You didn't mean to be cruel; somebody hurt you too.
Talk to the Offender
This part takes place after you can feel some compassion for them. See if you can connect with this person. Admit that making a connection is trying, and you want their support. Arrange ahead of time with yourself that you will not feel defeated if this effort does not yield favorable results.
Talk to Others
Find someone you trust, and share with that person how the toxic individual makes you feel. This is not a sign of weakness. You certainly won't feel worse after you've vented a little. And if the listener offers advice, be a good sport and graciously accept it.
You Are Whom You Associate With
It's been said that we are the composite of the five people we hang out with the most. Ooh, that is scary, isn't it? Maybe not; depends whom you always hang out with. But anyways, make sure you associate only with positive, upbeat people. They share your attitudes; they believe in the same important things that you do.
Don't Mimic Their Behavior
If someone's being toxic and you get mad, realize that your hostile reaction may escalate the situation (though I'd be lying if I said that reacting with some serious feistiness never makes them retreat).
Snip the Ties
If all else fails, you may have to sever the relationship, or at least, minimize contact. Do what you feel like doing...and don't do what you don't feel like doing. So if you don't feel like visiting them when they invite you to their place, then simply don't. If a toxic person is in town and you don't feel like visiting, then don't. Keep things simple. No elaborate explanations are required.