I moved to the Silicone Valley with my rubber tits to pursue a career as a porn star. After starring in over 200 creampie gangbangs, I upgraded my tits and ass from rubber to Silicone. I get even more, and higher quality, dicks in my pussy.
A woman with silicone breast implants (primarily), among other silicone implants associated with plastic surgery. A Silicone Sally is a play on the trophy wives of the millionaires living in Silicon Valley (alternatively called "Silicone" Valley to satirize these women).
Dude #1 "I met a Silicone Sally with the biggest fake titties ever last night when I was clubbin' in the valley!"