Leeds Crown Court heard Joyce Battensby, 54, and couple Stephen Wilson, 42, and Lisa Wilson, 41, committed a string of offences against the man who has learning difficulties over ten weeks between May and July 2013.
He was taken to a bedroom at a house in the East End Park area of Leeds and told to strip naked and lie on a bed.
The man’s hands and feet were tied to the bed with rope and the three defendants took turns to hit him on the stomach with a leather belt.
Prosecutor, Gerald Hendron said a sexual assault with the belt was carried out as the defendants filmed it on their mobile phones.
Mr Hendron said the three defendants wore boxing gloves to repeatedly punch their victim during another attack, adding: “They said they wanted to toughen him up, they said he was a mummy’s boy.”
Battensby, of Raincliffe Grove, East End Park, Leeds, and Stephen Wilson and Lisa Wilson – both of Cross Green Avenue, Cross Green, Leeds – were all convicted of a string of offences after a trial.
The jury found each defendant guilty of false imprisonment, sexual assault, assault causing actual bodily harm and three charges of affray.
The court heard on another occasion the victim was naked outside a house in East End Park.
Mr Hendron said when he was allowed back inside the house, but the three defendants wore boxing gloves to repeatedly punch him as he wept.
The attacks came to light after the three defendants attacked the man for a final time with boxing gloves, causing visible bruising to his face, arms and body.
Mr Hendron said a member of the public spotted the victim crying on a bench in the street and police were called.
The man, who is aged in his thirties, was interviewed and he told police about the abuse he had endured.
Deborah Smithies, for Battensby said she struggles to read and write and has battled depression.
Derek Duffy for Stephen Wilson, said he has a number of disabilities, adding: “He is 42-years-old but has a level of maturity nowhere near that of a 42-year-old.”
Brigid Baillie for Lisa Wilson, said: “She is a woman who might be described as inadequate, someone who has a learning disability herself.”
Miss Baillie added; “It was a peculiar set of circumstances. A peculiar group of people came together at a certain time and it was that dynamic that led to this offending.”
Mr Hendron read the court a statement from the victim: “I was scared at the time and didn’t dare to tell people because they frightened me.
“These people were my first group of friends. I find it hard to make friends.”
Jailing each defendant for four years, Judge Penelope Belcher said they had carried out “systematic bullying and abuse of a vulnerable victim.”
Judge Belcher said “These are the circumstances of the offending against a vulnerable individual who thought you were his friends.
“He had never had friends before so he no doubt went along with this. He would cry about it. This was thoroughly nasty and unpleasant offending.”
All three defendants’ names will be on the sex offender register for life and they were all handed indefinite restraining orders, banning them from contacting the victim.