Michael Swaim from Cracked/Those Aren't Muskets had the right idea.
"An asteroid that is without a doubt going to destroy every living thing on Earth"
The reasoning is that in the face of 100% certain death, no one on Earth will be fighting or arguing, leaving the last moments of life as a golden reason to hit on every single woman you meet.
Also, these quotes (paraphrased):
"All sports are cancelled, there's nothing on TV but clips of people crying, put me in you"
"You're not going to work tomorrow, no ones going to judge you and who cares if you get pregnant. Get in my god damn van."
"Sex is the last act for people to say "I'm alive". It's the last way to make a connection with another human being. Maybe even making a connection... in the butt. You know I'm right... Ass-pocalypse"
Best episode of After Hours ever.
Also discussed are why the zombie apocalypse wouldn't actually be an apocalypse and why a robot uprising would be horrifying.