Somali Abdul Yusuf, 31, has been carrying out violent sex attacks since he was 15 when he tried to rape a woman in the street.
Wearing an orange high-vis jacket, Yusuf grabbed a pregnant woman from behind as she boarded a bus in Finsbury Park, north London, a on 27 June last year.
The mother-to-be followed Yusuf while recording him on her phone.
Yusuf then carried out another attack while swigging from a bottle of Jack Daniels outside Finsbury Park station.
Claiming he had lots of money, Yusuf offered to buy her cigarettes and food before repeatedly suggesting they go to his home.
When she walked away he chased her, shouting out calling out “suck my dick.”
He pushed her to the ground, exposed himself and forced his fingers into her mouth, Wood Green Crown Court heard.
Yusuf, of Woodside Road, Wood Green, admitted two sexual assaults, assault by beating, assault by actual bodily harm and two counts of fraud.
He was sentenced to 52 months, with a four year extended licence period, and will only be eligible for release with the approval of the Parole Board after serving one third of his sentence.