Troy Maskell, 44, was handed a minimum five-year prison term on Wednesday, after being found guilty by a jury of manslaughter over the 2021 killing at a Shell service station in Victoria's north.
Strathmerton postmaster John Burke, 73, had smiled at Maskell's girlfriend and daughter as they entered the servo on the evening of August 8.
The woman then wrongly accused Mr Burke of being a pedophile.
Maskell was high on cannabis and drunk, after consuming a box of Carlton Dry and shots of Jack Daniels, when he picked up a bottle of sports drink and hurled it at Mr Burke.
The one-litre bottle struck Mr Burke in the head and he fell onto the hard-tiled floor.
Maskell kicked his elderly victim as he lay on the floor, and stomped on Mr Burke's glasses.
Mr Burke was taken to hospital but he could not be saved and he died after 11 weeks due to blood clots that developed on his brain.
Justice Lex Lasry condemned the killing as an "entirely unprovoked" attack on a physically inferior victim, and said kicking Mr Burke as he lay on the ground was "despicable".
"Yours is the kind of violence that society abhors," he told the court.
But he accepted Maskell had "genuine regret" about what had happened, suffered from PTSD and had served much of his time on remand in COVID-19 conditions.
He handed Maskell a maximum eight-year prison term and he will have to serve five years before he can apply for parole.
Maskell has already served 21 months of his sentence.
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