On May 8 last year, after being in the job more than a year, things came to a head in the smoko room, when company boss Kevin Hyde again questioned him about his sexuality.
When the young employee objected, Mr Hyde told him, "If you don't like it here, p*** off", the determination said.
He walked out and never returned.
Now, the worker - named in legal papers as Mr Y - has won his case.
The ERA awarded him $12,000 compensation for significant humiliation, loss of dignity and injury to his feelings and on-going ill health.
Hyde Engineering, who denied the claims, must also pay $15,795 in lost remuneration, $7500 in unpaid wages and $3500 in costs.
"His employer breached its obligations to him and it was reasonably foreseeable that any employee would resign in such circumstances, let alone such a young and reasonably vulnerable employee," ruled ERA member Christine Hickey.
Leeston-based Hyde Engineering, which the determination said is no longer in business, with Mr Hyde now in Australia, put it down to harmless "banter".
But Ms Hickey ruled: "Such language and behaviour of a sexual nature went beyond the bounds of reasonable banter that could be expected even in the all-male environment of an engineering workshop."
The ERA heard Mr Y got the job - his first out of school - as a 16-year-old in February 2011 with the help of a family friend.
He was made redundant in March 2012 because of a lack of work, but when the company got busier again, he was rehired in early May 2012.
Mr Y said he was sexually harassed by Mr Hyde, who knew he had Attention Deficit Hyperactive Disorder, and other workers during both spells at the company.
After he was "let go" the first time, he didn't want to return for a second stint but was pressured to go back by his parents, who were unaware of the bullying.
The youngster, who was paid just $10.50 per hour and wasn't given a contract, told the hearing: "I got a lot of BS from the guys, including Kevin."
Mr Y tried to stand up for himself, the determination said.
"Often I would just try to brush him off by saying pretty neutral things like 'yep', or 'righto', or 'ok'. They were all small words," he said.
"Occasionally I would turn to him and say 'you too', or 'you're the same', or things like that.
"Occasionally when he said rude things I told him he was being a dick, but I didn't use language stronger than that. He was the boss, and you don't really talk with that kind of stronger language to the boss."