Ditzy, I assume you know?  Stupid and airheaded.  "Central Casting" is a Hollywood-inspired term -- basically, if you're looking for the stereotypical villain or ingenue or another one-dimensional fill-in-the-blank character, Central Casting will send over someone to fit the bill.  Central Casting is actually a real casting company for extras, stand-ins and so on, but the name has come into wider use for stereotyped characters....