Scaffolder Darren Cole, aged 48, had held a grudge against Leon Hall, 45, for four years before launching the 'frenzied' beating, a judge heard.
The pair met by chance at The Staffordshire Knot in Pinfold Street, Darlaston, where Cole had also bumped into his 25-year-old landscape gardener son, Zach for the first time in two years, Wolverhampton Crown Court was told.
Mr Hall was set upon in the early hours of June 1 after going to smoke a cigarette outside the pub which had been screening a boxing match, revealed Mr David Lees, prosecuting.
Darren Cole followed about 10 minutes later and was heard to say to the victim: "Think you are hard? You are not as clever as when you beat me up, you b******."
He then grabbed hold of Mr Hall, who suffered from a kidney complaint, and punched him hard in the face up to eight times before Zach joined in by delivering more blows, continued Mr Lees who added: "It was clear the victim was unable to defend himself."
Both men then kicked and stamped on the head of Mr Hall as he lay motionless on the ground before leaving him unconscious in a pool of blood. Witnesses who tried to go to his aid were held back and told 'this is none of your business'.
Darren Cole allegedly told a woman after the attack: "He has been asking for it since he beat me up. I have waited four years to get him back." He then drove away with his son while Mr Hall was taken to the critical care unit at Birmingham's Queen Elizabeth Hospital to undergo emergency brain surgery and be put in a medically-induced coma.
Doctors said he had suffered long-term life-changing injuries that left him with mobility needs and memory loss that would prevent the gas fitter from ever working again.
Darren Cole was arrested at his home in Ruskin Street, West Bromwich, hours after the attack and his son, who lived in Highfields, Brownhills, gave himself up to police soon afterwards. The younger man later admitted taking cocaine and downing two brandies and five pints before the attack.
Mr Tim Sapwell, defending the father, said: "This was a moment of madness after a chance encounter. He bitterly regrets what he did and cannot adequately explain why it happened. They used to be friends."
Miss Alisha Harris, for the son, declared: "He is sorry for the pain he put the victim through. The attack was completely out of character. He took part in the offence out of misplaced loyalty to his father who he had not seen for two years before they met by chance that night."
Both defendants admitting causing grievous bodily harm with intent and were told by Judge Mark Eades: "This man was minding his own business, in poor health and in no position to defend himself. Darren Cole had a grudge against him and decided on a revenge attack which the son joined with vim and vigour. This was a ferocious, vicious and nasty attack that caused injuries way above what any grudge warranted."
Mr Hall said in a Victim Impact statement: "I was not expected to live. I managed to pull through but my life has changed permanently. Normal day-to-day things like making a cup of tea are a real struggle.
"I lost a large part of my skull and have to wear a protective helmet. I have to go back into hospital to have a metal plate in my head.
"This attack ruined my memory. I forget how to spell and the names of people. My right arm has been damaged and I struggle to wash the dishes.
"I used to be active and travelled all over the country with my job. Now I am unable to work and am struggling financially. I have gone back to my flat but I am not independent any more. Carers come in to cook and clean and I have to ask friends to drive me to the shops. I used to be a happy-go-lucky bloke but I am nothing like that now. These two men have destroyed my life."
His two attackers were also told by Judge Eades: "If this case had been heard 20 years ago, the chances are that he would have died and you would both be standing there on a murder charge."
"As it is, he underwent emergency surgery, was kept in a medical induced coma and suffered life-changing injuries. He can no longer work, will be disabled for the rest of his life and his memory is not what it was. It is a shocking state of affairs that all of this arises out of a grudge."