Apocalypse how: Your guide to handicapping the end of the world
Method of destruction: Ice
How that's going to work: An ice age is way too slow and undramatic at this point, so we're going to have to go with a rogue planet ripping us from our orbit to hurtle into deep space, freezing the planet solid. We'll probably have enough time for plenty of dramatic monologues as the planet gets colder and colder, and every unoriginal jackass still alive will point out the irony about how we were so concerned with global warming. On the plus side, our civilization will be perfectly preserved if some species of aliens finds us and wants to study and/or resurrect us, so don't be too surprised if you wake up five billion years from now in an alien zoo.
What it's going to look like:
Why that probably won't happen: We'd see a rogue planet coming, wouldn't we? Planets are pretty big after all. It's possible to argue that we're not looking in the right place, but c'mon. Planet. Frigging impossible to miss no matter where you're looking.
Odds: 5,000 to 1