According to prosecutors, Downey was hoping to get money to buy more crack. He had a ski mask but no gun, and so he stopped by the grocer's on the way to his target and bought a banana. Arriving at the bookmaker's shop, he concealed the fruit in a bag, pointed it at the two bookies and screamed, "I want the money or I will [expletive] shoot you."
That would be comical in a British accent to begin with, but even more so if it is fairly obvious that the robber has not a gun but a banana-shaped object that might in fact be a banana. That's what bookmaker Peter Humphrey immediately suggested to his friend, remarking, "He said he has a gun, but it might be a banana." Downey then produced a pair of scissors, which should have been more threatening except that by this point his credibility was completely gone. He got no money and fled the shop.
Police arrived quickly and found Downey still in the vicinity, struggling to get his too-tight mask off. According to the AP, a police dog found the banana, "badly bruised," lying nearby.
Downey pleaded guilty to one count of attempted robbery and admitted to "possessing an imitation firearm." The sentencing judge pointed out that "you did say, although it may seem comic now but not quite so comic at the time, that in the bag was a firearm," though "your victims having guessed what it was, [the attempt] was never going to succeed." Downey's lawyer unsuccessfully argued for a lighter sentence, calling his client's robbery attempt "farcical and incompetent."
Link: AP via SF Chronicle