Mark Green, 42, had been walking through Folkestone, Kent, last October with a group of friends including Victoria McNally when they bumped into another group which included 49-year-old Anthony Armstrong.
A court heard Mr Armstrong, who had just been to a food bank, ‘politely’ told Ms McNally: ‘Pull your dress down, I can see your knickers.’
Incensed, Ms McNally’s son, Ruben Smith, 19, threw a punch which hit Mr Armstrong in the face.
Green then stepped in and started repeatedly punching the victim in the head, causing him to tumble backwards into the road and smash his head on its concrete surface.
A woman who was accompanying Mr Armstrong said she saw ‘just so much blood’ as Green’s punches flew, and that the victim’s head ‘split open’ when he landed.
Green and Smith, who were known to Mr Armstrong, then pulled him onto the pavement and briefly tried to wake him up.
When he failed to regain consciousness, they tried to convince the witness to tell police he had slipped over, the witness told Canterbury Crown Court.
The 49-year-old was airlifted to a hospital in London but died three days later from catastrophic brain injuries.
Prosecutors said that, just 10 minutes before assaulting Mr Armstrong, the pair had launched ‘vicious, unprovoked’ attack on another man, Tristan Hanniford, outside of the food bank.
Smith, from Folkestone, admitted causing actual bodily harm to Mr Armstrong – but the judge ruled he could not be safely convicted of manslaughter after hearing how he stepped away after throwing the first punch.
He also admitted affray for the attack on Mr Hanniford and was jailed for a total of a year for both offences.
Green, also from Folkestone, admitted manslaughter but was found not guilty of affray.
A third member of the group, Kelly Bishop, from Hawkinge, Kent, is expected to go on trial later this year for alleged affray in relation to the attack on Mr Hanniford.
DC Tania Pickering of Kent Police said the incident ‘was an example of how mindless street violence can end in tragic consequences’.