.....No description needed.
Fail, fully known as failure, but people are too lazy to spell or say that much, is the act of people getting PWN3D by their own lameness.
Avatars are known to be masters at failbending, mostly because big guns up stares thinks kids should know no one's perfect. Aang in particular failed the entire series a lot, the biggest probably being his epic PWNage in Beijing Ba Sing Se. Afterward, he became briefly manic depressive. Wimp. Zuko is also a well known master of failbending. He failed at every thing you can fail at and more lots of things.
Whenever Zuko says anything, he is supposed to fail. He never fails to follow through.