Dont know if someone used it before, but it only just hit me (yes, i might be slow)
Step 1) Queue a random dungeon
Step 2) group disbands (or basically someone leaves)
Step 3) stealth in a middle of a pack that cant be killed usually with ninja pulls (i.e. two packs close to each other and patrol or something)
step 4) Afk.
Because you are party leader, when new people join via LFG they will spawn right on top of you. And since you are stealthed near a large mob pack.... yeah. instant carnage.
And if you cause these people to leave (im sure quite a few will after dying just as they port inside), you can requeue and repeat. over and over.
I had some fun earlier today, so much raging in heroic grim batol <3