Hallo Sargi
While your observation of the casual attitude shows a keen interest and observation on your part, the problem is that you cannot do anything against this person for what you perceive as their attitude, unless such attitude disrupts or influences the rest of your staff, staff events or performance. this is not the end of it though...
A perceived casual attitude is normally an indication of one of the following:-
1. In a social atmosphere, arrogance.
Causes:-
An inability to connect socially - This could be because of an underlying shyness, serious personal problems, being from another area or culture than the rest of the group, or a physical impediment that the person feels ashamed about. Remember that arrogance is normally a personal means of self-justification and a self-defense mechanism to keep others at a distance. It could also be an indication that the person regards himself as better than the rest, or feels intellectually superior to the rest.
Solution:-
Investigate - without the subject knowing (that will simply set up barriers) - what the root cause is behind the attitude.
If it is shyness, make sure to actively include the person in the group by asking his opinion, or relying on his participation in a public fashion.
If it is personal problems, try to find out more without being intrusive - simply reassure the person that as HR, you are concerned about him.
If it is a cultural problem, concentrate efforts to the group - in public - that in a work environment, all are equal and on the same footing.
If it is a physical impediment, ignore the condition, but increase the pressure on the person to participate.
2. Boredom
It is possible that this person is simply capable of much more than he is allowed to be, and finds the situation boring or menial.
Try to assess his talents and / or aptitude, and then compare his current level of work-assignment to his ability.
It is possible that he is simply not intellectually stimulated by the environment.
If this is the case, try to engage the person in problem-solving on his own level - challenge his intellect, and see whether that improves the situation. My guess is that his attitude will improve once he feels that he is delivering a more meaningful contribution.
If all of this fails, and you still feel that his attitude is being disruptive, put him through a conduct-councelling session, and follow the full steps to ascertain that the person does not feel that the matter is becoming constructive to his dismissal.
Hope this helps...