What's Up?

Everyday in my office I run into random people who almost always instinctively ask the same thing.
"Hey man, what's up?".
And I always blurt out "huh hey hi err hi".

The question "What's up?" has always baffled me. Now, you might go thinking that this is a very simple thing, something not worth spending a lot of time thinking about. But then when you are on bench for a long time, you tend to start questioning a lot of things.

What exactly do you mean when you ask "What's up?" ? Do you want to know what I have done in the past few days? Or what I am doing right now? Or perhaps you are weird and want to know about the stars and the sky?

Why I don't really like this question is, it immediately puts me under a lot pressure to come up with something cool. If I told you "Nothing da" which is really the truth, I just end up looking lame and boring. Lets admit it, I am not like some of my more out-doorsy colleagues who party every weekend and upload like 200 photos on Facebook daily. So unless I reply "ah just a bit tired after getting bit by a shark while practising scuba diving" you will remain uninterested and walk on.

Every time my manager asks me "Hey man, what's up?", I just smile awkwardly looking like a mute.  Somehow saying "I just finished Facebook stalking and came for a cup of coffee" didn't seem a better idea.

The even more weirder part is this conversation.
X : "Hey! What's up?"
Y : "Whaaattttt's uuuuuuuup?"
* End Of Conversation *
Seriously? Your answer to "What's up" is an elongated, more shrill "Whaaattt's uuup"?

The only possible conclusion I can get to is that human communication is an inherently complex phenomenon and not meant to be fully understandable.
Or I have had too much free time.