Towards the end of the first half, the banner, clumsily scrawled and with an unfortunate spelling error, was unfurled: "We weren(sic) that drunk."
Saint Aloysius Gonzaga, the Italian aristocrat and Jesuit brother who lent his name to the south Dublin school - and who can be presumed to have been in possession of exquisite copperplate - winced painfully before rolling in his grave.
Fresh from their escapades following their quarter-final victory against Roscrea in the Leinster Senior Cup on February 15 - when Gonzaga College's past pupils' union was forced to hit out against the "extreme drunkenness" and "offensive banners" - the fans in green and white were back. And, as it turns out, they are a lot more sedate when they are on the losing side.
Gonzaga were well beaten by Blackrock College in the semi-final, the scoreline 34-8.
But the 'old boys' put on a feisty sideshow - with a customised chant for this newspaper following a report that appeared last week about the angst caused by the behaviour of some of their number at the Roscrea clash.
"You can shove the f****** Indo up your ass," roared a small section of past pupils at yesterday's game in Donnybrook, with a supplementary verse of: "We hate the news."
The Gonzaga team is cheered on from stands. Photo: Damien Eagers
It was all harmless hijinks at the end of the day.
But their irritation can be traced by the internal email distributed last week to past pupils at the Jesuit school chastising a "small number of more recent past pupils" for reflecting "very poorly" on the school's past and current pupils.
"This includes extreme drunkenness, offensive banners, disrespect towards the opposition kickers, and some trouble on the streets after the game that resulted in gardaí getting involved." A Garda spokesperson confirmed one man was arrested for a public disorder offence in Donnybrook on February 15.
The email also asked for some of the older members of the union to keep an eye on the offenders during the semi-final against Blackrock - the first time Gonzaga have ever reached that stage.
A security guard removes pints at the cup game. Photo: Damien Eagers
"There'll be no trouble at this," he added.
One of the stewards was certainly confiscating a few bottles containing alcohol, and some cans of beer were hurled from the terrace, but there was nothing extreme.
Gonzaga fans are famous for their witty and boisterous chanting - a favourite being "we play chess" - and they kept a stoic, steady roar going throughout the game. Blackrock mustered a reply with: "Big, fat dirty boys, you're big fat, dirty boys."
But their rugby beef was helpless in the face of Gonzaga's half-time clown show.
Two of the old boys made their way into the centre of the pitch before another appeared with the blue and white of 'Rock on' over his own green. They wrestled and rolled in a parody of the game - with Gonzaga naturally coming out top.
A supporter jumps back into the crowd after running on the pitch. Photo: Damien Eagers
Amid all the confusion, one of the stewards got knocked down in a futile attempt to make a grab for them. Still, he seemed to take it in good humour and the crowd roared with laughter.
They needed their good spirits with the way the match turned out. Gonzaga scored the first three points but Blackrock replied and once they had the lead, never surrendered it. They will go on to play Belvedere in the final on St Patrick's Day.