This is not only my favorite joke because of the joke, but also because it was told to me by one of my favorite girls in a dive bar that smelled like pee, and I was rolling my own cigarettes back then and we were drinking $1 PBRs. I no longer do either but have fond memories.

ANYWAY. A piece of string walks into a bar and orders a pint. The bartender looks at him and says, "We don't serve string here." The string is really upset, but is determined to have a good time there, so the next night he kind of messes himself up a little, puffs up, and tries to sneak into the bar again. The bartender recognizes him and says, "I told you, we don't serve string!" The piece of string gets really frustrated, so the next night he distorts his body and ruffles himself up some more and goes back to the bar. The bartender looks at him, squinting, and asks, "Hey, you're not that same annoying piece of string, are you?" and the string looks at him and huffs, "No! I'm a frayed knot!!"