Dear Stefano,<quoted text>
Well, if someone pisses in front of their neighbour's door they do that intentionally knowing the consequences, unless in the moment of the performed act they were drunk.
Not really understood what did you mean by mental injury. As far as I know by mental injury is meant depression, stress, anxiety etc. They have nothing to do with what you said.
It's good question. Actually, I was expecting this question from you as I know that you belong to the western world. Actually, you are thinking from material aspect of feeling, but what "Krishna" talks is more of spiritual nature.
As you have rightly said, while pissing in front of neighbors door, the man knows very well about the consequences. But the definition of "Acts in the mode of Ignorance" does not consist of the word 'Knowing". It rather says "without concern ...."; that means simply knowing something, does not automatically make one "Good", but by acting on the knowledge in positive manner will only make one "Good". So, more important thing is Concern or, regard towards the consequence. Hence, although, that man knew that the consequence of his pissing in front of his neighbors door is not going to be Good, he refused to consider that possibility and acted in mode of "Ignorance".
For example, if you are attending an exam and you know all the answers, but you do not act on your knowledge. Will you score 100 / 100. No, you will fail ..... You will only get 100, when you will put down all the answers based on your knowledge. And only then it will be in mode of "Goodness". But if you think, what is the use, I know all the answers already, so I will not put down anything. In return you will get "Zero" and will be naturally termed as "Ignorant". So, you can see how this teaching applies to even today's situation. No, matter what is the age, these teachings are all eternally true and applicable as these are from "Krishna".
By mental injury, I meant, mental distress or, discomfort or, in simple term hurting the feelings of the neighbor. The Gita verse 18:25, talks about " .... or, distress caused to others ...", here distress can mean any kind of distress, mental or, physical ....