In my older rock-climbing days before I started office work, an 'Epic' was a climb (or entire climing trip) where things really failed to go to plan and you either had to extricate yourself from a life-threatening situation (over several hours) or more likely that you had to spend at least one night trying to sleep several hundred metres above the valley floor on a ledge barely wider than your ****. (One of the truly miraculous examples of this type of Epic was Joe Simpson)
Crucial to this though is that an Epic was something you got yourself out of and told well, made for an interesting camp story.
If you had to call in external support it wasn't an Epic, it was a pathetic embarassment and your mates would never let you forget it.
Now the word is used all over the place by people who have no idea. I think it was just the internet in general that wrecked it - everone uses "Epic Fail" to describe situations that barely rate as a Fail.