x and e^x were walking down the street when they saw a derivative up ahead.
"Oh, no!" cried x, "I've got to get out of here; that derivative will do me in for sure!" and ran off, fearing for his life.
But e^x just smiled smugly to himself and thought "Ha, I'm e^x, that derivative can't do anything to me." So he walked right up to the derivative and said "Hi, I'm e^x!"
The derivative smiled back and said "Hi, I'm partial/partial y."