Used to explain anything sexual when you are around older or conservative folks that don't enjoy open dialogue about sex. Origin comes from the Spice Network on DirecTV, which happens to be channel 596. Spice was once known as the pioneer of the ram cam, which ultimately led to its cult following. It can be used as a noun, verb, or adjective.
noun - That chick sucks like 596.
verb - I 596'd her brains out.
adjective - That slut is 596 loose.