This was a pretty tough decision this week, but I think I'm going to go with this Machariel:
This Machariel died thanks to the Screaming Meercats war-dec that happened this week. For an incursion Machariel, there's nothing particularly special about this fit. Other than relying far too heavily on buffer mods and that ridiculous Tech1 EM hardener, it's not all that different from a hundred other incursion Machs.
But this Mach didn't die in an incursion. It was ganked minutes after the first war-dec went live against Screaming Meercats.
I've talked about situational awareness in the context of a single PvP engagement. Know what you're fighting, and how, and if possible, why. Maintain awareness of the obstacles you might fly into that will hurt your speed or your transversal, or limit your ability to warp out of the engagement. Keep an eye on what your enemy is doing and try to counter his or her moves. All of these are basics for awareness of the tactical situation.
But you have to maintain awareness of the strategic situation, too. I don't know the full facts of this case. But I'll bet anything not maintaining strategic awareness was what happened here. This Mach pilot probably didn't bother to check whether his alliance was at war before he undocked. As a result of that, he was an easy, predictable target. I've said again and again that 100% of the fault for ship losses can be traced back to a mistake made by the pilot of the ship. In this case, the mistake this pilot made was undocking.
In null-sec, you learn to use your intel in a hurry. Before you undock, you check Local for neuts or war targets. You check your Corp or Alliance channel MOTD in-game. You probably check your corp or alliance forums, or ask on TS3 or Vent if anything is going on. Because if you don't do some or all of these things in null, you're going to lose a ship. High-sec pilots don't have these habits ingrained into them yet.
And this pilot just learned those lessons at the cost of about a billion ISK. That's an expensive lesson.
Runner-up for KOTW is this Basilisk, also from the Screaming Meercats war-dec.
Note to all incursion care-bears: just because incursion fits are kinda like PvP fits doesn't mean they are PvP fits. PvP fits have propulsion mods, for instance. ;-)