We are often called to stack with the tank, but invariably stacking with one of our tanks gets us killed and rarely the tank.  So it has become a running joke in our group that if you want to live, don't stack with that tank.  This addon helps to remind you not to stack with a particular player/target, and hopefully stay alive longer. :) 

This addon alerts you when you are standing too close to your target or focus.  It alerts you through text on the screen and (optionally) an alert sound.  How close is up to you. The default setting is 8.  There is another addon called RAFP_Options that allows you to configure alert distances, sounds, and messages displayed.  

So this was my first attempt to learn addons.  I took another addon (RangeDisplay) and started to modify their code, tailored specifically for this addon.