Epic- Anything great, spectacular, or large/monumental in nature
Fail- An inability to complete an objective, task or job either assigned or volunteered for.
Epic Fail -A mistake of such monumental proportions that it requires its own term in order to sucessfully point out the unfathomable shortcomings of an individual or group.
Jack: Uh, dude? I may or may not have wrecked 14 ferrari's with my moped after derailing a whole train carrying nothing but kittens and puppies...
Jim: Epic Fail, Man. EPIC Fail.