Poprawnie powinno byc "epic failure" poniewaz "fail" jest uzywane przewaznie jako czasownik. Zwrot "epic fail" jest slangiem.
Dictionary.com Unabridged (v 1.1) -
fail /feɪl/ Pronunciation Key - Show Spelled Pronunciation[feyl] Pronunciation Key - Show IPA Pronunciation
–verb (used without object) 1. to fall short of success or achievement in something expected, attempted, desired, or approved: The experiment failed because of poor planning.
2. to receive less than the passing grade or mark in an examination, class, or course of study: He failed in history.
3. to be or become deficient or lacking; be insufficient or absent; fall short: Our supplies failed.
4. to dwindle, pass, or die away: The flowers failed for lack of rain.
5. to lose strength or vigor; become weak: His health failed after the operation.
6. to become unable to meet or pay debts or business obligations; become insolvent or bankrupt.
7. (of a building member, structure, machine part, etc.) to break, bend, crush, or be otherwise destroyed or made useless because of an excessive load.
8. to stop functioning or operating: The electricity failed during the storm.
–verb (used with object) 9. to be unsuccessful in the performance or completion of: He failed to do his duty.
10. (of some expected or usual resource) to prove of no use or help to: His friends failed him. Words failed her.
11. to receive less than a passing grade or mark in: He failed history.
12. to declare (a person) unsuccessful in a test, course of study, etc.; give less than a passing grade to: The professor failed him in history.
–noun 13. Stock Exchange. a. a stockbroker's inability to deliver or receive security within the required time after sale or purchase.
b. such an undelivered security.
14. Obsolete. failure as to performance, occurrence, etc.