When people say bad things about me...behind my back...
Confront them. In public. Interrogate them, make them feel a fraction of what I feel on a daily basis.
And then generally cut them out of my life.
I've rarely had one of my good friends do such a thing, but I won't tolerate people being malicious for any reason. If there's anything I've learned, it's that I have to not be afraid of removing problems.