Rugby coach Dhanni Moar donned a pink costume for his fancy dress stag do in October last year.
But he took offence when party-goers dressed as Batman and Robin “taunted” him with derogatory comments regarding his sexuality.
A scuffle started and Moar was punched. But he reacted by carrying out an assault against the other man.
Moar, 28, of Aithsetter in Cunningsburgh was fined £600 at Lerwick Sheriff Court after he admitted pushing his victim to the ground and punching him repeatedly on the head.
Following the encounter his victim was left with a bruised lip, a swollen eye and a bump to the back of his head.
Procurator fiscal Duncan MacKenzie said the incident had been a “stupid drunken encounter”.
“Both parties had been out drinking, and both dressed in fancy dress.”
The court heard Moar had become the target of comments about his brightly-coloured dress after getting separated from his own group.
After pushing his victim to the ground Moar, who was the much bigger of the two, had the opportunity to walk away. He did not do that and carried on with the assault.
The complainer was taken to hospital suffering from his injuries.
Defence agent Gregor Kelly said Moar, a self-employed joiner, had been waiting in a fast food queue when the incident happened.
He said Moar had been offended when two men dressed as the super-hero characters Batman and Robin taunted him with derogatory comments about his sexuality.
Mr Kelly said Moar telephoned his victim’s parents the next day to apologise for his behaviour.
“Everyone could do without this sort of behaviour.
“He [Moar] keeps himself fit. He is a coach at the local rugby club. He keeps himself in shape and there was a disparity in size.”
He added Moar was punched first and should have been “man enough” to walk away.
“He tells me that he’s not really a drinker. Obviously this was a special day for him.”
Sheriff Philip Mann said Moar should expect to get a ribbing if he chooses to go out in fancy costumes.
“If you are going to go out in that kind of fancy dress, I think you have to be wise enough to understand that that is going to attract derogatory comments.
“Dressing up in fancy dress is meant to be a matter of fun, and if the other people choose to make fun of you and the way that you are dressed, that is something that comes with that particular territory.”
Sheriff Mann highlighted a previous conviction handed to Moar for assault two years ago.
“You would be well advised to watch your step in future.”