If above user's avatar showed up on your doorstep...

[Vrex360]

It's a human child so I'd probably send it off to the offworld security stations to undertake manual labor while I continue to burn it's planet.

 

[oppp7]

I would probably have a few seconds to scream before I get cut up by lightsabres.

 

[RanD00M]

I would wonder if hes here for the revenge or the coffee.

 

[Pm0n3y]

Oh, Sup Xandus?

[sup][sup]did you bring the weed?[/sup][/sup]

 

[oppp7]

Damn, ninja'd...
Well, I'll shoot your avatar then... (after you kill me and I get better...)

 

[XIII's Number XIV]

Me: AAAAH!

Him: AAAAH!

Me: AAAAH!

Him: AAAAH!

 

[Mcupobob]

What the hell is that!!! then I would put it in a test tube.

 

[Mister Awesome]

"ahhhh, come right in"

 

[Pm0n3y]

OH SHIT! The Flobots are on my front porch! *squeals like a fangirl*

 

[Metric Monkey]

"Alright, who left this bag of flaming popcorn at my doorstep!? Lousy kids and their pranks these days." *grumble grumble*

 

[Roxas1359]

Why is there a manatee on my doorstep. Crap, I got to get you back to the zoo before i get in trouble.

 

[Kiba Bloodfang]

I'd invite you in to play video games

 

[I Stomp on Kittens]

Damn! These things always follow me home from school..

 

[Metric Monkey]

Oh wook at da wittle kitty and- Oh my god is that a freaking missile!?!

 

[I Stomp on Kittens]

The sound of it hitting the glass and visualizing this at the time would probably lead me to saw "Ahh! WTF?!"

 

[Code Monkey]

Great, now that NeonBob's done with the whales, he's started nuking kittys.

 

[Dark Knifer]

I'd turn it around and close the door behind it.