Though there have been many periods of debauchery and louche behavior, I think it's hard to draw a direct line of causation between Ancient Rome or Weimar Germany or Pre-Hays Code Hollywood to '00's bimboism but...
When did bimboism start?
I believe it had its roots in the period from 1953-1966.
Hugh Hefner founded playboy in 1953 and published nude photos of star Marilyn Monroe who starred in the same year in Gentlemen Prefer Blondes and How to Marry A Millionaire, both huge hits. Being a nude model, while still risque, was no longer a barrier to success and prestige. Reinforcing that trend, Jayne Mansfield posed for Playboy in 1955 and several times thereafter and was named Golden Globes promising newcomer of 1957. So posing nude had lost some of its
A good summary by Jeff Little can be found at http://www.loti.com/hubba_hubba.htm:
"By the mid 1950's, stars like Mamie Van Doren (High School Confidential) and Jayne Mansfield (The Girl Can't Help It) had opted to ignore the current craze of 3-D movies in favor of double-D attractions. And while such homegrown starlets inflamed the hormones of American males, imports such as Brigitte Bardot (And God Created Woman) set men totally ablaze with even less inhibitions concerning the baring of flesh on screen."
In 1962, Marilyn Monroe sang Happy Birthday Mr. President to John F. Kennedy in an unforgettably sexy performance.
In 1966, Memoirs v. Massachussets liberalized laws on pornography, making it virtually impossible to prosecute obscenity and opening the door to the flood of porn that hit America's newstands shortly thereafter.
The stage was set.