In English, we often use the term "when pigs fly" to indicate something that will never happen. It's become so common that we've managed to make flying pigs a pop culture meme. It's not the only way to say it in English, and other languages have their own colorful phrases for "not gonna happen." For example:
Israel "When hair grows on the palm of my hand"
Hungary “When it’s snowing red snowflakes”
Portugal “In the afternoon of Saint Never’s day”
There's more of these at Nautilus, and even a world map showing where more idioms are used. Link -via Phenomena
(Image: T-shirt available at the Neatoshop)
Kids these days may only know flying pigs as those recoiling after being hit by Angry Birds, but I know better. I got a Gund Flying Pig (with a little motor that flaps it wings, but does not get it airborne) from Woot! some time ago. And years before that, I had a Nerf Football with a piggy snout, ears and tail (the only web evidence of such a thing is this picture of someone else's). Of course, there's also Breadpig, but wings made of bread have questionable aeronautic capability (unless they're California Sourdough).
Kapag gumuho na ang mundo (When the world disintegrates).