The teenager was being baited in a clash with Swansea City's Liam Cullen in added time at Vicarage Road with the home side 2-0 down, and responded to a shove by reacting wildly with both hands raised to the midfielder's neck and pushing him over.
It was a wretched finale for Watford, whose hopes of pushing towards a Premier League place have taken a hit since the start of the New Year as they've slumped to 10th, now four points off the playoff places.
But it's even more of a setback for the talented 19-year-old Irankunda who, after the brightest start to the season with his spectacular free kick goals, hasn't started a match for the Hornets since November and doesn't appear to have the full confidence of his now under-pressure boss Javi Gracia.
The manager had talked on the eve of the game of how the Australian youngster was still important to his plans, but his unnecessary red card on Saturday after he'd only been on as sub for quarter of an hour, will now mean a three-match ban which will doubtless have infuriated Gracia.
It's not the first time Irankunda has seen the red mist when being wound up or fouled by defenders. He also got sent off when at Adelaide United in November 2023 for raging at the referee after not getting a call while being constantly niggled by Melbourne Victory markers.
Watford have now failed to a win in five matches in all competitions, their worst run of the season, prompting a miserable Garcia, who only returned to his former club in October, to explain afterwards that he was now planning to talk with the club owner Gino Pozzo.
But for a struggling Swansea side featuring another Socceroo, Cameron Burgess, this was a much needed boost, thanks to goals from Marko Stamenic and Josh Key.
Another Australian international with reason to cheer was Riley McGree, who was back in title-chasing Middlesbrough's starting line-up after a recent injury absence and helped them earn a key 1-0 win over Norwich that takes them level on points at the top of the table, second only to Coventry City on goal difference.
McGree teed up Hayden Hackney to have a crack on goal in the 17th minute, and then watched the Boro skipper curl home a beauty which ultimately proved enough for them to carve out a fifth consecutive victory while Coventry, who'd been 10 points clear at the top late in November, lost 2-1 at QPR.
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