Let me give you an example where I want this "mystery" word to fit. There are two person "A" and person "B". A had installed an air conditioner in his house long ago and has called in the customer care services for servicing it. B is the technician who went to A's house for troubleshooting. As per the rules, A is supposed to show the purchase bill to the technician after he finishes his job. But A had kept the bill in his office and even though A knew this was mandatory, he still did not bother to bring the bill because he thought that once the job is done, it cannot be reverted back to it's undone state and B would have no choice but to return back to the station with disappointment and anger because of the customer satisfaction and user experience policies which requires him to be polite and friendly to the customers. So he(A) is reluctant to bring the bill and he doesn't care about B. He just wants AC to get fixed. Mind you, A is not lazy.
So, the sample sentence is:
This was an act of _______ on the part of A.
One word that springs from my mind is "unjust". I am not sure though. Other ways to describe the situation in a sentence?