Lee Graham carried out the lewd act while sitting just a matter of feet away from the woman, causing her to flee the Stagecoach bus in horror.
The 26-year-old got off the bus soon after but was snared by police after his shocking behaviour was captured by on-board CCTV.
When quizzed by police, Graham said he had the ‘urge to do it’ after spotting the woman on the bus.
Graham, of Chirton Avenue, South Shields, admitted an act of outraging public decency at an earlier hearing at South Tyneside Magistrates’ Court.
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The matter was adjourned in order for a probation report to be compiled on Graham ahead of sentencing.
He was slapped with a blanket ban from using bus services in the borough until his return date in the dock.
Clare Irving, prosecuting, said; “A woman was sat on the Stagecoach bus at Prince Edward Road when the defendant sat close to her.
“She believed he was off his head on drink or drugs and said he was staring at her.
“He put his hand down his trousers.
“She was shocked and disturbed and got off the bus.”
Graham told police ‘he was off his face on heroin’ and could not remember much about it.
In a statement read in court, the victim said: “The incident left me disturbed. I was worried he would follow me and sexually assault or rape me.”
Christopher Brown, defending, said: “He did not expose himself but has behaved in an outrageous manner.”
Magistrates handed Graham a 14-week jail term - suspended for 12 months - and ordered him to pay compensation of £250.