The Playboy Mansion would be crawling with hookers and celebs on Thursday nights back in its heyday -- and a new documentary claims Hugh Hefnerhimself cooked up the weekly event.
Hef dubbed the traditional gathering "Pig Night," and it started with 2 pimps bringing in carloads of prostitutes from Sunset Blvd. ... according to his former girlfriend, Sondra Theodore, and others who worked at the mansion.
Sondra says she tended to look the other way while Hugh did all sorts of "crazy stuff," but this ritual stood out to her and got her attention.
The upcoming A&E series, "Secrets of Playboy" ... describes "Pig Night" as a sort of dinner party that served as a jumping-off point for sex parties.
According to the mansion insiders, Hugh would sit at the head of the table smoking his famous pipe while the hookers drank and ate with movie and TV stars. They say the girls would get ratings and quick medical checks before slipping out of the room for sex rendezvous with the celebs.
While folks in the mansion knew what Hefner and his cohorts labeled the evening, they say he insisted the prostitutes were never to be called pigs -- nor were they told what everyone around them was calling the event ... behind their backs.