Is it Christian, or Biblical to "Slander" a Former Member Of Your Church?

No church that is following the teachings of Christ would slander any individual. Insults are not Christ like. Now we as believers are responsible for being honest to each other when we are offended by someone but this is to be handled in a respectful way with in the body of the church. Then the issue is not be played out in public but forgiveness and atonement are worked by all parties. I hope you find a church that is Christ centered!