I did a quick search and didn't find anything on this. This is my first contribution so please don't be hard on me.
What you need is a warlock with a Succubus and the spell Seduction.
1. Put your pet on aggressive.
2. Target the person / npc you want to kill.
3. Put seduction on auto cast (right click)
4. Your pet should now be casting seduction, right click the spell seduction so it isn't auto-casting and then when the spell has been fully casted your pet will run and start attacking the friendly target.
Tested on The Murloc Village Twink server.
Works on any friendly targets.