Smartbutt comments I use in everyday scenarios in reply of things:

What are you up to?
*gestures to the top of my head* I'm up to here.

Because that's the way the cookie crumbles.
But why does the cookie have to crumble? I mean, what if someone wants to eat it as opposed to have it just crumble? Or why just hasn't someone really gone in depth, all sciencey about it? Like, Isaac Newton wanted to know why things fall, why can't people wonder why the cookie crumbles? Or are we in like, a 1984 world where people aren't allowed to think for themselves?

What's up?
Well, there's the ceiling, the sky, the troposphere, the stratosphere, the mesosphere, the thermosphere, the sun, the planets, the stars, whatever's not been discovered in this galaxy, whatever's in other Galaxies, and other galaxies after that, and after that, and after that... But you also have to consider the fact that Earth has no definitive relativity in space, so I could also say the ground, the soil, the mantle, the crust, the inner core, the outer core...

Or:

Whatever's not down is up *walks away*
(I generally use this one, because the former takes way too much time that nobody's got)

What's cookin'?
Um... the chicken?

What did you do over the weekend?
Nothing.
Well, you had to have done something. You can't have done nothing.
I suppose you're right, I'm sorry. Okay, I first opened my eyes on Saturday morning, yawned, stretched some of my limbs, and took a long sigh of bliss. I then proceeded to get up from my bed after a few minutes or so of lying there and disconnected my phone from the charger. After that, I checked my emails, my wattpad, and you know, the usual. On Instagram, my friend replied to my comment, so I replied back. And then she replied to that comment, so I replied to hers. I kind of chuckled a bit - I mean, no way is Zayn hotter than Leo Valdez, am I right? So, this prompted me to rant about Zayn, about how obsolete he is when compared to Leo. And then she got all angry at me and started writing out a rant as well. So, then... *continues a two hour long description of my weekend*