Gordon Sawers threatened to carry out violent sexual assaults on youngsters during the incident on board the vehicle which was travelling between Kilmarnock and Ardrossan.
The 46-year-old pleaded guilty to five charges when he appeared at Kilmarnock Sheriff Court in November last year.
The Stagecoach bus was pulled over by police in Kilwinning on February 25.
Sawers accepted a charge of communicating indecently with teenage girls, another of indecently causing a youth to hear sexual communications and threatening her with sexual violence, along with an offence of public indecency.
The incident took place at around 4pm on the day, procurator fiscal depute Fraser Alexander told the court, when Sawers was travelling on the double-decker bus, sitting in the rear seats upstairs.
During the journey, a group of girls came on board and sat together close to where Sawers was located.
“Sawers then began to engage the girls in conversation. Very quickly this turned onto a sexual conversation,” Mr Alexander told the court.
“To be clear, it was the accused only that was making any sexual references.”
(Image: Facebook) The prosecutor then detailed a number of specific explicit remarks made by Sawers, who is now described as a prisoner at HMP Kilmarnock, towards two of the group.
He told the pair “I will take you to my house and s**g you”, adding “I will inject you with heroin” before warning he would “get with your maw”.
Sawers made further comments which were directed towards the youngest member of the group.
He stated that he wanted to perform a sexual act upon the girl and told her “I’m going to rape and stab yous and that”.
The court heard that Sawers then proceeded to perform a sex act on himself, causing the youngsters to be “distressed” and “visibly upset”.
It was at this stage that another passenger who was travelling on the bus informed the driver of Sawers’ conduct – with police immediately contacted.
The bus pulled over on Pennyburn Road where officers attended and traced the offender.
He was arrested and taken to Saltcoats police office where he was cautioned and charged and made no reply.
At his sentencing hearing on Monday, January 13, his solicitor Sandy Currie told the court that Sawers described his actions as “banter”.
He said: “At the time he had a chaotic lifestyle including drug use, which led to his behaviour and the seriousness of it.
“I can’t begin to explain or excuse it. He accepts he has very little recollection of what he said and did.”
Sheriff Nicola Patrick said: “He appears to have deliberately targeted the young girls. Because of the seriousness of these crimes, a custodial sentence is the only appropriate disposal.”
Sawers was jailed for two years and was also sentenced to two years on license following his release, meaning any further offending would result in further jail time.
He was placed on the sex offenders register indefinitely, due to the extended sentence handed out.
Sawers was also sentenced to a year in jail for a range of other charges, which will be served concurrently to his two years behind bars.