Gentlemen: I shall never shave, for the same reason that I started a beard, and for the reason my father started his. I remember standing at his side, when I was five, while he was shaving for the last time. “Father,” I asked, “Why do you shave?” He stood there for a full minute and finally looked down at me. “Why the hell do I?” he said.

George Bernard Shaw (1856-1950) British playwright and critic
(Attributed)

Postcard response when invited by an electric razor company to shave off his beard with their product.Variant:
  • "I was about five at the time, and I was standing at my father's knee whilst he was shaving. I said to him, 'Daddy, why do you shave?' He looked at me in silence, for a full minute, before throwing the razor out of the window, saying, 'Why the hell do I?' He never did again."