It's a phrase uttered by those entirely confused by the concept
  of their parents having had sex to conceive them. They just
  can't fathom it.

  It's the answer to existence.

  "Why am I here? Is it God? Randomness? Is there a purpose to my
  existence? Why? Why? WHY AM I HERE!?!?!"

  "Oh, you know why you're here. Your parents they... you know..."

  "What, the fuck?"

  "Yeah, they had sex."

  "The fuck?"

  "Yes. The fuck."

  WHAT THE FUCK!

  And so it began, a lifelong cycle of cognitive dissonance, never
  to be fully resolved.