Well, this is one I hadn't heard of before, but sounds hilarious.
You probably already know about
International Talk Like a Pirate Day, but did you know about
Pretend to be a Time Traveller Day?
The idea is to basically pretend you're a time traveler, from the past or a possible future (be it
utopian or
dystopian). There is, however, one catch: You can't directly tell anyone you're a time traveler!
My personal favorite technique: Walk up to random people and ask "What year is this?" When they tell you, get all quiet and then say, "Then there's still time!" before running off.
The fun starts on Monday, December 8th!