William Doyle (18), whose girlfriend is expecting his first child, was arrested by gardai after the woman who had ordered the pizza recognised the three youths and contacted gardai.
The 36-year-old victim, Binu Sebastian, was rushed to hospital by ambulance, where he was treated for a cut to his scalp and a superficial wound to his back.
He had been hit over the head with a bottle, stabbed in the back with the bottle after it had been broken over him and kicked when he fell to the ground.
Doyle -- previously of Clondalkin but with an address at Solas House, Talanstown, Ardee, Co Louth -- pleaded guilty at Dublin Circuit Criminal Court to the unlawful seizure of a vehicle on Kilcronan Avenue, Clondalkin on June 25, 2009.
His 13 previous convictions include public order and criminal damage offences.
They related to a period between 2009 and 2010, in which his defence counsel, Pieter Le Vert, said his client was "out of control" owing to his addiction to ecstasy.
Judge Patricia Ryan imposed a one-year sentence which she suspended for three years after hearing that Doyle has kept out of trouble in the past year.
Garda Declan Bambrick told Cathleen Noctor, prosecuting, that Mr Sebastian was about to drive away having just delivered the pizza to the house, when he was approached by a youth who demanded his car keys.
He was about to comply when he was dragged from the car and beaten. Doyle and one of his accomplices, jumped into the vehicle, while a third youth continued to beat the victim, until the car engine was started.
He then jumped into the car with the other two and they sped off.
Gda Bambrick said the houseowner, who witnessed the incident, was warned by one of the gang that if she called the gardai she would be "done".
He agreed with Mr Le Vert that Doyle came from a respectable family and that his girlfriend of three years is three months pregnant.
Gda Bambrick accepted that Doyle has since turned his life around and put this matter behind him.