Omar Thompson, 19, of Herne Hill, south-east London, hit Det Con Mark Glicksman, 30, in May last year after he was told off for being rude.
Thompson told Southwark Crown Court he acted in self defence at the Surrey train station, but was convicted.
Det Con Glicksman was left with three metal plates in his face.
Lying unconscious
The off-duty officer had been out drinking with colleagues before getting off a train at Carshalton train station, in Surrey, when Thompson "barged" into him.
When the officer commented there was "no common courtesy anymore", the college student lashed out with a single blow that left him lying unconscious in the station subway with three "serious" fractures in his jaw.
Thompson, who was convicted of grievous bodily harm, told the jury he was afraid he was going to be pushed onto the train tracks by the officer.
But as commuters ran to his victim's aid, he was heard to say under his breath "yeah, but he was disrespecting me".
"You showed no concern for your victim"
The court also heard Thompson falsely claimed to have been racially abused by Det Con Glicksman.
Sentencing, Recorder Michael Supperstone, said: "You struck a single blow with such force that you caused very considerable damage to his jaw. And his pain and suffering has continued.
"You showed no concern for your victim. It is clear that you decided to teach him a lesson because in your view he had shown disrespect towards you.
"In my judgement your offence was so serious only immediate custody can be justified."
Thompson will serve his sentence at a young offenders institution.
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