Five times the size of an average penis would give you a thirty inch penis. I'd imagine it would get embarrassing when your erection exposes itself between your cleavage. And then you might need a ball strap to hold onto your giant testicles, for support, but that's a different story.
Oh, and if you with your giant-five-times-the-size-of-normal-testicles gets busted and your nuts swell up and can't fit into your ball harness...as if they were big before, now busted and swollen! Huge!