Revenge is a simple tool that is designed for PvP realms in mind, to easily keep track of the latest aggressors, and add them as your Rival. No need to worry about Arenas or BG's filling this list up; Revenge is disabled in these places, and only active in the Open World (hopefully).
In order to open the window, either click the pin icon on bottom left (which you have to add there first, via the list menu that shows up when you click bottom left button), or use the slash command, "/revenge".
An example is shown above; "Tipsiz" is a "friend" who has recently attacked me, and via Revenge, I can easily add them as a rival, to hunt them later on. Rivals will not show up in this list, neither the players you dismiss. In the second screenshot, you can see how tooltip of the pin icon looks, telling you there is a rival nearby, and who it is.
If you don't know how to pin an add-on, either check the screenshots, or click the bottom-left button, which opens a list of add-ons that supports pinning. I hope you find this add-on useful.
If you encounter any problems, please copy paste the error, or take a screenshot showing the oddity.