Two strings went on a pub crawl one evening.
However, they had wandered into a part of town that didn't cotton to strings very much, and they had a hard time getting served. They would go into a pub and order beers. The bartender would look at them and say, "We don't serve strings around here! P*ss off!!", and would throw them out.
This happened over and over, again. Finally, they decided to separate, so that they might be less recognizable.
The first string went in to face the suspicion of the bartender. The bartender asked, "Aren't you a string?". The first string stammered and stuttered, and ended up in the street.
The second string also tried his luck, but only after disguising himself by rolling in mud, dirt and mire and generally making himself look scruffy.
Again, the bartender looked closely and asked, "Say, aren't you a string?".
The answer came, "No, I'm a frayed knot.".