Angry Kevin Fowler, 46, (pic.top) picked-up and threw 39 year-old software account manager Adrian Farthing's laptop bag at him, prompting a confrontation on the late-night commuter service.
"It is always sad when two professional men wind up in an absurd dispute about a bag left on a seat in circumstances where it leads to violence," announced Croydon Crown Court Judge Timothy Stow QC.
"This was a ridiculous dispute. It should never have reached a point where there was physical contact.
"The defendant was positively drunk and was far more aggressive and we are quite satisfied he simply lost his temper when Mr. Farthing laughed at him.
"There is no way laughing mockingly can justify a physical attack.
"He punched him hard on the top of the head, forcing his face forward onto the tray in front of him."
Father-of-two Fowler, of Withdean Avenue, Goring-by-Sea, Worthing, who told the court he had spent £50,000 in legal fees fighting to clear his name, was previously convicted of assaulting Mr. Farthing on the London Bridge to Brighton service on August 4, last year.
When quizzed by police after a night in a cell he complained: "I'm a middle-aged, middle-class bloke standing up for the rights of rail travellers, who have a right to use a seat."
He sold his company after the conviction and is now employed as a management consultant.
"This gentleman came in, picked-up my laptop bag, and threw it at me," Mr. Farthing (pic.bottom) told the appeal. "An arrogant throw in my direction.
"He said he bought a ticket for the train and had every right to sit there.
"I asked him why he was being so vulgar and rude and he said: 'You'd better fucking shut up.'
"He was very slurred in his speech and appeared to be incredibly drunk.
"I had a laugh at him in a mocking way and I believe that inflamed him because the next thing that happened was that I received a blow to the top of my head.
"It was a very violent blow and forced my head down and I suffered a cut to my eye. I assume the cut was caused by the tray in front of me and it split the skin open an inch and a half.
"My coffee spilt all over my lap. At that point I was in a state of shock."
Mr. Farthing denied he was trying to protect his personal space on the crowded train by also pulling down the tray behind the seat next to him and placing his coffee on it.
The pair got off the train at East Croydon station and talked to police. "He was looking rather pleased with himself," said Mr. Farthing.
Fowler told the appeal he had approximately four to five pints after a training day in the City of London, but was not as drunk as witnesses described and claimed Mr. Farthing was the trouble-maker.
"He was condescending, patronising, sarcastic, passive aggressive," said Fowler. "He was playing games and he laughed at me."
Fowler admitted striking out in self-defence when Mr. Farthing made a sudden move towards him.
"I was just instinctively looking to protect myself. I was not looking for trouble, I was with colleagues and a long way from home, the last thing I needed was any hassle."
Fowler's sentence of a twelve month community order, including 200 hours community service work remains, along with an order to pay Mr. Farthing £1500 compensation and £550 magistrates' court costs and £500 appeal costs.