"Double Whammy" comes from the old comic strip =Li'l Abner=, by Al Capp. There was a character named Evil Eye Fleagle (sp?) who could curse his enemies by staring at them: this was referred to as "putting the whammy" on them. The "double whammy" was one variant. Fleagle's eyeballs would bulge, and he'd lean at an angle and the target character would be struck by some kind of disaster. The term has entered common speech as a synonym for a particularly evil curse. I seem to recall that Fleagle was from Brooklyn (or some such exotic locale), and wore a zoot suit.