"So You Think You Can Dance" judge Mary Murphy is a desperate, drug-abusing sexaholic ... who's addicted to plastic surgery ... so says her former manager in a new lawsuit.
Murphy is being sued by her ex-manager Michael Sanchez -- who claims he was hired as Murphy's personal manager in 2006 ... and practically saved her life ... only to be kicked to the curb in 2010.
In his suit, Sanchez claims Murphy was a NIGHTMARE ... and he was constantly covering up her dangerous and scandalous behavior to protect her image.
Among the claims, Sanchez says Murphy is a "desperate, cocaine-fueled nymphomaniac" who had "many inappropriate sexual relationships with 'So You Think You Can Dance' and 'Chelsea Lately' crew members."
Sanchez claims he once busted in to her apartment when she was unresponsive ... and found Murphy high on drugs and in bed with a SYTYCD producer ... with cocaine on the nightstand.
Sanchez also claims Murphy would violate FOX TV rules and U.S. game show laws by secretly coaching contestants behind the scenes.
And there's more -- Sanchez says Murphy would be drunk on set during tapings and hide her booze in a Coke cup.
But despite his loyal service to Murphy, Sanchez claims the judge breached their contract and fired him in 2010 after a dispute over money.
Sanchez says Mary stiffed him on commissions ... and he's demanding more than $1,000,000 in damages.
So far, no comment from Murphy's camp.