Mine's Battlefield 3. Nothing even comes close. I love Battlefield. I played the shit out of Battlefield 3 despite my hatred for it. Everytime I turn it on, it takes at least 10 hours of constant rage 'til I've sufficiently vented my frustration with pretty much each and every design particular of this game, so that I can somewhat enjoy it for the Battlefield game it is. But god, do I ever hate this game. So fucking much. Black tar of hatred is oozing from my soul everytime I touch it.
So what's your most hated game ever? Remember - there's no hate, if there isn't love as well.