Okay, this is what we have so far for the reasons the world, as we know it, will end:
Meteor
Black Hole
Gamma Rays
Nuclear War
Regular War
Religious War
Superbug
TV
Antichrist
Catastrophic release of Carbondioxide
Massive Vulcano Eruption
Massive Earthquake
Abortion
Gay Rights
High Taxes
The Poor Get Poorer
Excess Liberals
Hillary Healthcare
Social Conservatives
Fascism
Demagoguery
Surveillance Society
"Nation Building"
Chemical Contamination of Food and Toys
Overpopulation
...
and all of the above at once!

Might have missed a few major ones.