Blurry,
* I use deaggro poison, at Grandmaster level.
* If a Paladin uses Amends on me, he dies. We've been there, I know.
* I'm usually grouped with a Warding healer to dodge AE's; they would hopefully not get aggro even with my transfer, but I don't like risking the death of a healer.
* Read the description on the Cowl of the Villain carefully - it procs when YOU, the wearer, get hit.
This last point I haven't personally tested since I have a Nemesis Hood (far better stats) and no real interest in the Cowl UNLESS it works contrary to my belief. But, if you read the description of the item carefully, it's phrased to say that it procs when YOU get hit. Our Brigand has his "de-aggro" hat, and he steals aggro anyway as well; this is practical data if not particularly scientific.
I know exactly when I steal aggro without parsing: Almost every single battle, when the MAIN TANK or MAIN ASSIST call "Full Burn," I die 5 seconds later. Yes, I do de-aggros first. Yes, I use Concealment to decrease the aggro I'm getting. Yes, I use the above mentioned Grandmaster Ignorant Bliss. Depending on how quickly I get off my stealth attacks, sometimes I use Decap while Concealment is still active... but if it ISNT, then I wait til at LEAST 1 of my 2 de-agg's has refreshed, and I use it before using Decap.
There is nothing more that I can do for myself to control aggro unless I'm wrong about the way the Cowl works. Nobody else in any thread I've posted this same problem has mentioned the Cowl, and I made no indication that I'm using one... so, I am assuming that the Cowl functions in the matter I've interpreted it.
(Otherwise, I'd have a lot of Assassins going "GET YOUR COWL U NOOB OMG!!" and that hasn't happened *grin*)
-Hadanelith Raswrolski, 70 Assassin of Kithicor