"Who are you?" and "What are you doing here?" are two questions to which the correct reply is extremely important to know. Consider:

You break into somebody's house in order to steal their grandfather clock. They walk in on you in the process. As they're rubbing sleep from their eyes, they cry, "Who are you, and what are you doing here?!"

Wrong Answer:I'm here to pillage, rape, and plunder!
Wrong Answer:I want to suck your blood! (although it becomes slightly more right if you use a phony Hungarian accent)
Wrong Answer:I found a treasure map on the tongue of a dead man, and it lead me here!
Wrong Answer:Arry, matey! Yer landlubber questions be confusin' this old pirate!

Right Answer:I'm the grandfather clock inspector (the cousins of which, "house inspector," "stereo inspector," and "wallet inspector," are all good answers too)
Right Answer:(while waving your arms around in the air) This is just a dream! Go back to sleep, sweet spirit! (this works best if you imitate the backwards talking bit from Twin Peaks and dance all around)
Right Answer:Don't panic. This is an alien abduction. Close your eyes, and the anal probing will be done within a minute. (while the interuptter's eyes are closed, skip town (unless you want to commence with anal probing))