July 17 - the date shown on the iCal icon all year round. When it finally comes around, Apple geeks around the world celebrate by wearing clothes adorned with the iCal icon.
Jim: Hey Bob, happy iCal day! I made this glowing iCal T-shirt specially for the occasion!
Bob: That's nothing, I have an iCal thong on right now.
Jim: Wow, what a brilliant way to honour His Steveness!