During my travels through happy happy pony land, I've came upon a very uncharacteristic background; the grave of Pancakes.
Who is Pancakes, and why is his grave in the land of endless joy, sunshine and dismembered unicorns?
Currently, there is no reliable information or source about the tombstone inscription or its meaning.
Some people pointed out that the inscription is an anagram for "A Epic Prank" (however, missing the letter s), which could be seen as a reference to Trolling is a art: The purpose of this phrase is to troll people by getting them to correct it (example).
A little OT: Blizzard put some stuff into the game where the purpose of is not known by now, e.g. the Black Rock Ledger. There exist long discussions about it. Perhaps the tombstone will also turn out to be another clue to something bigger.