I agree with Chrisam-crystals. If you know who it is, then ask that they be
shown the error of their ways --lovingly. You don't want any bad karma coming back to bite you on the backside. Send lots of loving thoughts and
do protect yourself.
All of the above suggestions are great, I carry angelite with me, so conflicts will be minimized or dissolved before they even happen. I also surround myself in a bubble of white light.
Also call on Michael and the other archangels to protect you from negetivity.
Blessings,
Shadow Wolf