From my own personal experience, the best thing to do is start to distance yourself from this person. Don't totally blow them off or they might start rumors about you. Just be nice and slowly back...
you can not completley get rid of them but you can make it so they arent around YOU. all you have to do is simply go up to your friend and tell them you dont like that other person. if this doesnt...
You get a little red icon say (1) on the top far left corner of your screen. You can click on it and see who it is, then click either "Confirm" or "Ignore"