Three strings are going out for a night on the town.

The strings go to a popular bar and the first string walks up to the bar and says to the bartender, "Hey, barkeep! Three beers, please!"
The bartender starts to pour three beers when he turns to the string and says, "Wait just a minute. Are you a string? We don't serve your kind here!"
So the string turns and walks back to his friends and tells them the bad news. The second string tells his buddies, "don't worry about it. I'll get us some drinks."
The second string goes up to the bar and orders three pints. Again, the bartender turns with a scowl on his face and says, "listen, I already told your friend, we don't serve your kind here."
The string turns back to his friends and tells them that he, too, failed to get their drinks. The third string, fed up with all of this nonsense storms outside. His friends watch as he rubs his head against the brick wall outside. Before coming back inside, he twists himself around like a pretzel.
The third string then goes up to the bartender and orders his three drinks. The bartender turns to him and says, "hold on, are you a string too?"

"No, I'm a frayed knot."