A piece of string tries to get into a bar.
"Sorry mate", says the bouncer, "No pieces of string allowed".
The piece of string can't believe it. He gets angrier and angrier, twisting and writhing on the ground, tangling himself up, tying himself into knots and rubbing against himself. After doing this for a while he calms down and tries to get in.
"Look mate", says the bouncer, "I told you no pieces of string. You're clearly a piece of string".
[drumroll]
"No" says the string, "I'm afraid not".
geddit?