I have always thought that 1 Peter 3:16-17 referred to non-believers speaking evil of believers. As I read this today, I realized that I may have been narrowing the field of slanderers more than the text calls for.
The context of this Scripture passage seems to indicate those of faith, not non-believers. In verse 8 we are given the directive to "be of one mind, having compassion for one another; love as brothers, be tenderhearted, be courteous; not returning evil for evil or reviling for reviling, but on the contrary blessing...." This is quite clearly speaking of the household of faith, in spite of the fact that it mentions evil against a brother and reviling against a brother.
I have at times been the recipient of such evil, reviling, and slander. And I have been the originator of such things as well. This scripture tells us how we are to handle such things when we are the victim: "be ready to give a defense to everyone who asks you a reason for the hope that is in you, with meekness and fear; having a good conscience, that when they defame you as evildoers, those who revile your good conduct in Christ may be ashamed."
It is hard to not seek revenge against those who have slandered and misrepresented you. It is hard to maintain a humble and meek spirit when brothers in Christ commit evil against you. It is even harder to to bless them during these timesbut that is exactly what we are commanded to do (v. 9).