Nick Kennedy did not mince his words as he described the incident that saw London Irish captain David Paice sent off during Gloucester's 39-15 Aviva Premiership victory.
Irish hooker Paice saw red when he drove his shoulder into the head of home scrum-half Willi Heinz on the stroke of half-time.
The tackle is likely to bring Paice a considerable ban should he be found guilty at a Rugby Football Union disciplinary hearing this week and director of rugby Kennedy said: "It was a definite red card. Unacceptable for our group.
"We pride ourselves on our discipline and he really let the team down, going down to 14 men.
"I watched it once back and it was a red card. The referee got it spot on."
At the time, Gloucester were 20-8 up after tries from flanker Lewis Ludlow and fly-half Billy Burns. Gloucester added three more after the break, with Burns getting his second plus touchdowns from flanker Jake Poledri and wing Henry Purdy. Centre Billy Twelvetrees added two penalties and four conversions.
Irish's points came via a try in each half from prop Petrus du Plessis and lock Teofilo Paulo along with a penalty and conversion from fly-half Tommy Bell.
Kennedy thought Irish, who have only won one of their 10 Premiership games this season, were in with a chance at the time of the Paice incident.
"We were very much in the game and a few elements were going well for us," he said. "If we had gone in with 15 men, we would have been happy with the half and looking forward to the second half.
"But all those plans go out of the window when you have 14 men."
It was Gloucester's fifth straight Premiership victory under head coach Johan Ackermann, who only came into the role a few weeks before the season started.
Ackermann said of the bonus-point victory: "To get the five points is a bonus and it keeps the momentum there.
"The biggest thing is we ground it out tonight. It was not pretty but we showed we can go down in that arm wrestle.
"But I will not lie to say I am pleased with the way we have played. We had a lack of intensity and accuracy but it is mixed emotions because you have to be grateful that you have got over the winning line and scored 39 points."