The son of Pink Floyd guitarist David Gilmour shouted "We're going to break all the laws" as he went on the rampage at a student fees protest, a court heard.
Charlie Gilmour pleaded guilty to violent disorder in May after joining thousands demonstrating in London.
During the march on December 9 he was photographed hanging from a Union flag on the Cenotaph, a caper for which he has since apologised.
He appeared for sentencing at Kingston-upon-Thames Crown Court in south west London accompanied by his rock star father and mother Polly Samson, who watched proceedings from the public gallery.
Their son covered his face with his hands and smiled in embarrassment as the court was shown footage of his antics.
He was first caught on camera in Parliament Square waving a plastic bag containing food. Here he was heard to shout: "'Let them eat cake', they said. We won't eat cake, we'll eat fire and ice and destruction."
Other footage depicted the Cenotaph incident and showed him elsewhere waving a red flag on a pole and raising his scarf in an apparent attempt to partially hide his face.
Prosecutors told the court the 21-year-old had that evening leapt on to the bonnet of a Jaguar car driving up Regent Street in a royal convoy containing the Prince of Wales and Duchess of Cornwall.
Gilmour was accused of throwing a rubbish bin that appeared to hit the Jaguar, but his defence disputed the allegation. The student had no recollection of throwing the bin and there was no evidence he had done so, his barrister, David Spens QC, said.
Gilmour was also accused of attacking the front window of Topshop's flagship store in Oxford Street and making off with the leg of a mannequin that had somehow come into his possession.