It's such an annoying question. Here's how to answer:

1. "The ceiling."
2. "The sky. With a few clouds and 37.4% chance of rain."
3. "Outer-space and UFO's"
4. "Same old grind."
5. "Today is the same as yesterday, which was the same as the day before that, and the day before that, and the day before that, and the day before that..." (continue until they leave)
6. "My rent"
7. "My middle finger."
8. "What's not up? Well, besides my salary."
9. "Iceland's economic crisis."
10. "Gas prices."
11. "The chances of you dying alone and miserable."
12. "Your cholesterol level."
13. "It was all good till I saw your face."
14. "Oh, that is SO cool. I did not know that 'What' is up today. Was it down yesterday? I'm so glad they fixed it."
15. "Well, I'm not dead yet. How about you?"
16. "FML."
17. "My mood swings."
18. "Well, I'm kind of down lately. My doctor finally took me off the meds."
19. "What's it to ya?"
20. "You're one of THEM, aren't you?! They sent you here!"
21. "That's confidential information."
22. "I'm socially programmed to say 'Not much. What about you?'"
23. "Well, your face is the highlight of my day."
24. "Well, I was just standing there hoping I wouldn't be asked another stupid question, but I guess that's not going to happen."
25. "Do you hear that?.....That's the sound of no one caring."
26. "I'm trying to imagine you with a personality."

Google