A piece of string walks into a bar, and the bartender says to him, "Hey buddy! We don't serve pieces of string here! Can't you read the sign?" And he kicks the piece of string out of the bar.  

So the string is outside the bar, and decides to create a disguise for himself to get inside.  He ties his head in a knot, and brushes out the end on top and walks confidently back into the bar and sits down.  

The bartender walks up to him handing him a drink, and looking suspiciously at him, says "Hey... weren't you that piece of string I kicked out of here just a little while ago?"  

The piece of string replies, "No, I'm afraid not!"