While adults are just starting to notice, usually with disapproval, "fail" used as a noun (as in "That's an epic fail."), my students are already racing ahead and converting it to an adjective.
We can tell that "fail" has become an adjective because it can be preceded by the quantifying adverb so, as in "I'm so fail." [Cf. I'm so happy (adj.), but *I'm so student (n.)].