LOL.
This is a good one:
You need two people: You and a friend. Both have to look at the sky at a crowded place. Suddenly, because of human's curiosity, one will come and try to discover what you're seeing. He/she will eventually ask either you or your friend about what are you looking at. The one who was asked will tell:
"I don't know. I saw this guy here staring at the sky about 10 minutes. I'll ask him."
Then, suppose the one was your friend. then he'll talk to you:
"Excuse me, what are you staring to?"
"Me, I'm not staring at nothing..."
"Of course you are. Why are you looking at the sky all this time?"
"Ah, this. I'm with a painful torticollis and I can't fix my neck..."
Be sure to tape it!
A more funny, but watch out!