"I felt that we did not play what we trained all week so it was pretty disappointing."
The only salvage work was the bonus point they claimed when Rene Ranger scored a crushing late try after some strong team lead-up work.
But that cohesion was rare for the Blues in a match they needed to win to stay unbeaten with the Brumbies and Sharks.
Kirwan accepted responsibility for the inconsistent preparation and the lack of sting which followed mixed training sessions.
The Blues bumbled their way to a 6-15 deficit at the interval but when they nudged into the lead after Charles Piutau's try in the 52nd minute, the 25,112 crowd sensed some value for their Sunday appearance.
That only served to rev up the Bulls, with flanker Arno Botha scoring a glorious team try and Morne Steyn goaling enough kicks to get his side home.
Blues skipper Ali Williams said his side wanted to use the ball and stress defences but had got sucked into the arm-wrestle the Bulls favoured.
"We lacked some real spark," he said.
That had to come from the players, not the coaching staff.
"I am the same as JK. I am pretty pissed off at how we played, purely for our attitude to play Blues rugby."
The Blues have a fortnight to stew on their work before their next game, against the Waratahs in Sydney.
