A rather annoying word whose use in certain situations has greatly increased recently.
Kind of like the word "shit," "fail" is used by people who don't stop to think of a better word to use, making them pretty much useless to society.
A kid falls off a bike.
Douche bag: Fail!
Person that can think rationally: Stop saying "fail" at people who weren't even trying to succeed at anything in the first place.