Hey, what's up..buddy!

1. Human 1: Hey! What's up?

Human 2: " hey! Going on" (most common response, Iam more or less sure 99% of people say that)

2. Human 1: Hey! What's up?

Human 2: "The sky" (smart person answer: also: "the ceiling" or, "da roof")

The second one sounds more like my son.

There are some annoying social protocols that are non-rational (i.e. not irrational, but not rational, either -- just there). This is one of them. I find it quite irritating.

Sometimes I suspect, most people who say this phrase(or equivalents, like "How's it going?") don't want a true, non-terse answer. They simply want to fulfill the "mutual acknowledgement protocol."

Believe me, in my case it could lead to few minutes of nerve-wreaking mysterious silence, or if you really take the initiative, it could lead to a nice conversation.

It's bothered me before because I couldn't answer it. But depending on the situation, "what's up" will be interpreted differently.

As such, I stick to neutral and short responses which is socially acceptable. "Not much. How 'bout you?" "Great day. Hope you're having one too." "Enjoying the weather." "Looking forward to the weekend." Or anything along those lines.

I generally vary it up, sometimes coming up with a date-specific response in advance. Otherwise you risk appearing unfriendly due to a disingenuous/unoriginal/stock response.

I find it peculiar.Sometimes, the wrath on their face builds up as they know they are approaching the answer which they weren't willing to gather with great interest anyway. At other times, it is fuelled by a comical 'I-dont-know-what-else-to-ask-you-first' look pasted on the face. And them I imagine, either they quite don't enjoy knowing me or obviously the person asking is either bored and wrote 10 messages like that to other people, or has little imagination.

I have special affection for people who come up with an endearing 'how are you doing! Hope you are well! So nice we meet today!' It's almost romantic and filled with an assurance that the person did indeed like seeing me.

Over the years however, my expectations are stoically aligned with the larger choice. And I gradually adjusted to the knowledge that..the most common answer to what's up is “I am fine, thank you, what about you?” 

I have begun to assume that irrespective of what the person who is asking intends, they are enquiring about my well being, at that very moment.  And as for my answer..yeah! I have worked on a bunch of alternate responses, sometimes hilarious, based on the age of the person. It may start from a 'Life is good' ...or a 'not much, what's up with you?'...to 'same 'ol'...and then inching towards a pressing 'everything that's supposed to be' or an ouch! 'we're gonna find out soon enough'. And there is always that person to whom I might say..'aah! Shit you know... living the dream!'