Who could have guessed that a sneering, meglomanic, Aryan child of incest would make for such a convincing villain? Born of Lannister lovin', Joffrey succeeds his 'father' Robert to become a king more concerned with mutilating prostitutes than ruling the Seven Kingdoms.
In the end his crazy behaviour does lead to an embarrassing incident with food at his wedding (awkward!) but not before he is able to satisfy the psycho killer's fun-time checklist. His most heinous crime, aside from being a total wang - was, by unanimous decision, ordering the execution of Eddard Stark.
Apart from fulfilling Sean Bean's cast-iron death clause, this is where - despite his supreme incompetence - Joffrey made a decision which the realm is still reeling from, especially the north (at least until The Winds Of Winter comes out). His act of heartless, cackling villainy set in motion the events that would bring us multiple Stark tragedies like the Red Wedding, Jon Snow's surprise party and Sansa acting as a damsel-shaped lightning rod for punishment.
He may have lost the Game of Thrones (let's be honest who hasn't by this point?), but it was on his orders that the Direwolf's head was removed and even now it's few remaining limbs are twitching aimlessly - with no resolution and little in the way of direction.