When does a higher command step in?

Too little information for a judgement.

That said, I have found that most of the time when a conflict occurs there is a least some concern that the person has drifted into a behavior that requires notice. And often the individual is unaware that he/she has done so.

Regardless of which side I have been on, I always try to analyse what, if anything, I have done or not done to contribute to the situation.

IG will only step in if they get a complaint, so make it happen if there is a significant issue. You'd better be righteous though. A higher command will only act when they believe something is sooooo wrong that it requires intervention. That is rare, as mediocrity is not an excuse for removal from position or intervention in a grander scale. The view from above is different from the view from below. I have had subordinates who are hated by their subordinates, but only because of mediocrity and failing to meet their expectations. Being below average happens and it isn't necessarily a reason for dismissal. Counseling will happen in an attempt to change the officer/NCO, but if it doesn't work, it will take upwards of 12-18 months to remove someone for general under-performance. Someone has to do something wrong in a big way to be relieved. The only other option is the IG. If it is that bad, someone has to make that call. Preferably, multiple calls from multiple people about the same issue.

If you let things slide, they will continue to slide. Have you talked to him about it? Have you talked to the PSG/1SG about it? Not making excuses, but sometimes the person in question may not realize they have crossed a boundary. As a courtesy saying "Sir, you got a moment?" may fix the issue. If it doesn't run it up the flagpole to the IG. Then when it rolls back down hill, there are no surprises, because you did talk to them.