Green Arrow singlehandedly tracking down Prometheus to his other dimensional lair and instantly killing him with a single wooden arrow when Prometheus had been able to shrug off other much more powerful attacks throughout the series.
Complete Monster: Prometheus started out as a Magnificent Bastard in his initial appearance when created by Grant Morrison. He then went on to suffer severe Villain Decay in most of his follow-up appearances... until now. In his grand return after years of limbo (after a special one-shot used Final Crisis to retcon all of the non Morrison/Villain Decay stories involving the character as being an impostor), he unleashed a wave of chaos, carnage, and torture on the heroes of the DCU that rivaled even the worst Big Bad in the worst Crisis, murdering countless D-list superheroes, killing Mikaal Tomas's lover and Congo Bill's pride, sewing Freddy Freeman's lips together to keep him from speaking his magic world, cruelly lobotomizing genius IQ, mutilating Red Arrow, and culminating with murdering 90,000 people in Star City, including Red Arrow's little daughter; all because, as a kid, his criminal parents were shot in front of him by the police. The series may have been incredibly criticized, but there's no denying that Prometheus is easily one of the most monstrous characters in the DCU.
Memetic Mutation: An unfortunate font choice made the title look more like "Gay for Justice" at a passing glance. Naturally, this caught on fast.
As mentioned on the trivia page, while he did do a fairly lackluster job overall, Lian Harper's death was not James Robinson's fault (Executive Meddling strikes again!), although it's one of the first things people usually blame him for.
A fair number of fans, and even people who aren't comic book readers, have conceded that Robinson's statement at San Diego Comic Con 2010 that he was inspired to cut off Roy Harper's arm as a tribute to Iraq war veterans by creating a superhero with a prosthetic that's not cybernetic was both in very bad taste and an utter dick move, regardless if this was honesty, a bold-faced lie, or something his editors told him to say. He contradicted this statement in the introduction of Cry's trade paperback, saying that the editors told him they wanted to put Roy in this direction. He also made absolutely no mention of his statement at San Diego.