One of the stupid questions I hate.

[Mr Hero]

Bonus points if the customer complains about their food being cold

[DaisyQueen]

"Who is it?!"
"Basket of puppies!"

[AyreBiskits]

Candygram for Mongo!!!
Candygram for Mongo!!!

[dbuzman]

"I am become Death, the destroyer of worlds."

That might get their attention.

Here's another good one.

"I am created Shiva, the Destroyer; death, the shatterer of worlds. The dead night tiger made whole. Who is this dog meat that dares challenge me?"

[Aethian]

Another reader of Master Chiun and his idiot son Remo! Squeeeeee completely unrelated my favorite book of the series is "Angry White Mailmen"

[RootedPhoenix]

"Who is it?"

"Batman."

[Jay 2K Winger]

"Who is it?"

"Batman."

No, that response is best reserved for the question "Who are you?"

The only other acceptable response to that question is, "Hello, my name is Inigo Montoya. You killed my father. Prepare to die."

[Mr Hero]

Who could that be? I say, "Who is it?"
No answer
"Who is it"
There's no answer
"WHO IS IT?"
They're not saying anything.

So, finally I go over and I open the door and just as I suspected. It's some big fat hermaphrodite with a Flock-Of-Seagulls haircut and only one nostril. Oh man I hat it when I'm right.

[Geek King]

Who can it be knocking at my door?
Make no sound, tip-toe across the floor
If he hears, he'll knock all day
I'll be trapped and here I'll have to stay
I've done no harm, I keep to myself
There's nothing wrong with my state of mental health

[XCashier]

"Who is it?"
"It's the plumber! I've come to fix the sink!"