one day in mathstown, e^x was happily plotting (functions dont plod, they plot) along the road, when he heard nearby screams. Suddenly the constant C came shooting out into the road screaming his head off. "Argh" he cried, "SAVE ME", he screamed. e^x was confused, and asked C what the matter was...to which he replied "It's a derivative, he's escaped from Calculus Island and is differentiating everyone, I'm doomed....doooooooooooooooooooooomed, save yourself!". e^x however, was very calm, he replied "I'm e^x, i'm derivatives can't harm me!"...so he set off in search of the derivative. He followed the trial of mass differentiation and eventually found her, wildly differentiating the poor constants, and multilating the defenseless simple functions. e^x aproached the derivative and said "Hello, I'm e^x", to which the derivative replied, with a slight smile, "Hello, I'm d/dy"
the above is possibly the worst maths "joke" i have ever heard anyone ever tell me!