A train guard stationed at Waterfall who was sacked after sending a picture of his penis to a female colleague was not unfairly dismissed, the Fair Work Commission found.
This was despite the "dick pic" being sent while the man was at home and using his private mobile phone.
In February 2018 Rodney Fussell sent a image via Snapchat of his erect penis to fellow train guard Kendall Abbott, who he had known since 2012.
Ms Abbott, who said the image was unwanted, sent it on to several other work colleagues and it came to the attention of Sydney Trains management.
After an internal investigation, Mr Fussell was sacked on August 15, 2018.
While the "serious misconduct" occurred when Mr Fussell was at home and using his personal phone, it was judged to be a breach of the Sydney Trains social media policy.
The policy stated that employees "should ensure that the conduct is consistent" with professional standards and ethical principles.
"It was put by Sydney Trains that the offending image, while sent outside work hours and not involving a work device, still had a connection with the workplace," the Fair Work Commission (FWC) decision released late last month stated.
Mr Fussell claimed he had "inadvertently" sent the dick pic - intending to send a picture of a tattoo instead - and immediately contacted Ms Abbott to apologise.
However Ms Abbott said they had been talking on social media and he said words to the effect of "When I am drunk I send naughty images".
She told him "do not send me a picture of your dick", which he soon did.
Immediately afterwards, he said to her on Snapchat. "Shit don't look. I'm so sorry".
Mr Fussell claimed his dismissal was unfair because he sent the image in error and "immediately sought to remedy the situation".
"It was put by counsel for Mr Fussell that the punishment does not fit the offence as the dismissal was disproportionate to the sending of a single explicit image to a person outside of the context of the workplace on an accidental basis from a private mobile phone," the decision read.
FWC Deputy President Geoffrey Bull said he was "satisfied that the offending image was deliberately sent and Mr Fussell's attempts to suggest otherwise strain credulity beyond any reasonableness".
While it may have been a one-off lapse of judgement "the image was at the extreme outer limit of offensiveness", he said
Deputy President Bull found the misconduct was in breach of Sydney Trains employment policies.
"It therefore constituted a valid reason for termination," he wrote in his decision.