Felipe Contepomi's late penalty condemned Ireland to an agonising 29-28 defeat on the eve of their tour to New Zealand - and just days after the Barbarians were comfortably dispatched 57-26 by England.
The Kingsholm crowd of 11,654 were firmly behind the Barbarians as the invitation side contained a number of players with Gloucester associations and they were deserved winners.
The Irish were deprived of their Leinster players - resting following their defeat in Sunday's RaboDirect PRO12 final - but despite their absence, a better performance would have been expected.
"We are disappointed," Kidney said. "The Barbarians were a lot better than they were on Sunday against England.
"They were well focused, it was a tough game and but we only went down to a penalty three minutes from the end.
"We didn't have a full deck of cards but it was a brilliant opportunity for some of our fringe players."
Kidney is due to name his squad for the New Zealand tour later on Wednesday and reported no major injury worries after Tuesday night's match.
"No one has been ruled out," he said.
"I'm going to discuss players' conditions with the medics over the next few hours. I know Mike Ross has a tight hamstring and he may struggle for the first Test."
Ronan O'Gara, the Irish captain for the night, added: "In the first half we struggled but we felt we were getting it together by the end.
"A lot of what we did was good but we didn't do it often enough."
Asked about his side's chances in New Zealand, O'Gara said: "It's a huge challenge; it is the survival of the fittest.
"Test rugby takes you out of your comfort zone and people don't understand that it's a whole new level and it's going to be extremely tough."
Mike Tindall, the out-of-contract Gloucester centre, had an impressive game for the Barbarians, scoring one try and having a hand in two of the others.
Barbarians coach John Kirwan said: "Mike has been fantastic. He was very good on Sunday and at 33 he wanted to back it up tonight by playing on his home ground.
"With Francois Louw he was the player of the day. He has great rugby nous, is a fantastic competitor and I'd be signing him up as he's great at going forward and if you look after yourself, you can play until you are 35 or 36."
The Barbarians now face Wales on Saturday and Kirwan added: "The game is all about Shane Williams.
"It will be his last ever match playing against Wales at the Millennium Stadium.
"All the squad want to play and it's a question of picking the right team."
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