Sidiq Shenwari flew into a rage when a 27-year-old man, who walks with a stick, showed him two fingers as he crossed the road outside Rotherham train station, on May 16, last year.
"The defendant pulled up on to the pavement, got out and shouted: "Why did you stick your two fingers up, you f****** idiot?" prosecutor Carl Fitch said.
"He took a golf club from the boot of his car and ran at him with the golf club in both hands and hit him extremely hard on the bottom of the back.
"He fell to the floor, dropping his stick and his shopping bags and was left rolling around in pain."
In police interview, Shenwari, who has no previous convictions, denied hitting the man but agreed he had been there and had an argument.
Chris Aspinall, mitigating, said: "He is extremely remorseful and realistic and has insight into his behaviour that day."
Shenwari, 29, of York Road, Eastwood, Rotherham, pleaded guilty to assault occasioning actual bodily harm and possession of an offensive weapon, at an earlier hearing.
Judge David Dixon told him his victim could have put up two fingers to say: "Give me two minutes to get across the road, I'm a bit slow.
"You seemed to think it was an abusive gesture. This was classic road-rage."
He sentenced Shenwari to 18 months in prison.