I think that the odds are so miniscule of any of those, it's a tie.
1: The world ends tonight/tomorrow/at some point on the 21st of this year.
This is such lame shit, oooo the Myan calander, oh my god, really? Most religions in history had some ties to this exact time of year based on astrology, I give no fucks.
2: A human sets foot on Mars before 2023 (so, in the next ten years, for you math geniuses)
Yeah right, take a lot longer then that.
3: The Soviet Union is reformed, and invades the United States.
Is this cereal? Didn't think this was even a topic for discussion, did I miss something?
4: Comrade Obama sends the Feds out to collect and melt down all civilian owned "Assault Rifles".
Even if Obama sets it in motion our government will take way too long and someone else will get credit, not gonna happen.