Hi, how are you today?

Fine, thanks for asking.

Which is the normal response one gets when asked that question.
I, however, work in a dentist office, and I can't decide if people are actually grumpy all the time, genuinely hate life, or just hate the dentist office.

Patients walk in and I greet them with a smile and ask them how they are. They usually grimace, roll their eyes, nod, or have lost their hearing and reply with: 'No, it's not raining yet, but it's threatening to."
All right then.

Other responses I've received:

"I'm here, aren't I?"

"Fine, until I walked in" (how nice)

"Alive"

"None of your business" (fair enough, I guess)

"The right side of Tuesday" (what?)

"I'll be honest with you, I drank some whisky before coming here"

No one is ever happy to see you at the dentist office. And when they leave they usually have a frozen mouth and can't talk or have taken 3 Valiums and a little left of center.

Outside of the dentist office, a lot of people ask how you're doing and don't actually listen to the answer, or on the flip-side, they ask you and REALLY want to know. They want to get in deep with you and talk about your childhood  or their bowel movements (both painful) and you're all "thanks but I don't really know you that well and you have some mustard on your chin and that's all I can focus on right now"

I worked in a grocery store once where the first rule was DON'T ask how people are doing because they will tell you, and this will cause a line to form. But it's my first instinct to, so I would always end up saying "Hi, how are you...uh, your potatoes, they look real good, um, that will be $4.67, here's your receipt...erm, kthanksbye"

So no matter who you ask or how they are be prepared for any kind and length of answer. Be prepared to listen, ignore, or get distracted by the errant piece of fluff on the bridge of their nose. (How do they not know it's there??)