The guy being sued is Dr. Allen Metzger -- who went on tour with MJ and even videotaped the singer's wedding to Debbie Rowe. He also testified at Dr. Conrad Murray's manslaughter trial. According to the lawsuit ... which reads like a bad Penthouse Forum letter ... Metzger got realllly handsy with a patient named Victoria Oliver during a 2010 exam. Oliver claims ... during one physical exam she asked if everything was OK ... and he responded, "Delicious" ... referring to her body. In her suit, filed in L.A. County Superior Court, Oliver claims he escalated his gropiness in 2012 ... when he placed his hand under her blouse. Oliver claims she protested ... but Metzger responded, "Why don't we close the door and really have some fun." Oliver claims the doc then complimented her shoes ... and then snuck around behind her and groped her breasts from the back while pressing himself against her body. In her suit, Oliver claims she was humiliated ... and says she now suffers from mental anguish and emotional distress.