A constant function, c and e^x are walking on Broadway.

Then suddenly, c sees a differential operator approaching and runs away.

So e^x follows him and asks why the hurry.

"Well, you see, there's this differential operator coming this way, and when we meet, he'll differentiate me and nothing will be left of me...!"

"Ah," says e^x, "he won't bother ME, I'm e to the power x!" and he walks on.

Of course he meets the differential operator after a short distance.
e^x: "Hi, I'm e^x"

*****  POOF *******

diff.op. with a sinister laugh, "Ha Ha Ha..., I'm d/dy"