had code words and signals that he used with a boy he allegedly molested to describe various sex acts ... including "duck butter."
James Safechuck -- now 36 -- claims in his lawsuit against the MJ Estate ... the singer started abusing him when he was 10 ... when he traveled with Michael to Paris for the "Bad" tour in 1988.
In new court docs -- obtained by TMZ -- Safechuck says Michael taught him to use code words ... referring to his erection as "bright light, brick city" ... and calling semen, "duck butter."
Safechuck claims Jackson also used secret signals -- when they would hold hands, Michael would scratch the inside of James' hand with a finger ... to show he wanted to have sex.
Safechuck says MJ wanted a full-blown relationship with him ... to the point he performed a secret wedding ceremony with the boy with wedding ring and a marriage certificate.
He also describes how Michael would take him to various homes -- including a place called "The Hideout" in Century City -- where they would drink sweet, pink wine and watch porn ... including movies of children masturbating.
Safechuck says at one point ... he questioned his own sexuality -- because he also had a crush on Sheryl Crow, who was one of Jackson's backup singers. He says Michael found out and became jealous ... showing him unflattering pics of Crow without makeup.
Safechuck says the abuse stopped entirely when he reached puberty.Howard Weitzman
, attorney for the MJ Estate, tells TMZ the whole lawsuit should be scrapped because it was filed more than 20 years after the incidents supposedly happened ... and says Safechuck "has given sworn testimony that Michael never did anything inappropriate to him."