The story
Blend of Revenge of the Sith + fifth. From the name of the Star Wars movie Episode III – Revenge of the Sith and a day of the month most similar sounding to "Sith".
Etymology from Wiktionary, CC BY-SA 4.0.
Revenge of the Fifth
Today it means: The Fifth of May (May 5). The second Star Wars Day, the day after May the Fourth (May 4). Sometimes used to celebrate the Dark Side, when May 4 is used to celebrate the Jedi. Full definition →