Regardless, the first step has to -- has to -- be directly engaging him about the concern personally.
Respectfully, offline, in a non-threatening way. That direct engagement may go nowhere and even result in a negative response, and if that's the case, then take it to the next level.
I see far too many folks (in life, not just in flying) who are just plain too frightened to directly engage people about these kind of things. Either they don't want to antagonize the situation, or they don't want to face personal embarrassment for themselves or the other guy, or are afraid of the result of bringing it up, etc. They'd rather go to that other guy's supervisor or to another organization, and let someone else take care of the problem. It is the workplace analog of passive/aggressive spouses who won't just tell you when something is bothering them. It is also a little like the cultural aversion folks have to shaming someone else or being shamed themselves.
This isn't what we should be doing as pilots. It isn't fair to the person who is doing something incorrect or offensive or unsafe to not directly tell them the truth (again, you can do this and still be tactful and respectful). Good CRM, real professionalism, isn't going behind someone's back and telling on them.
Again, absolutely nothing might result from talking to them about your concerns personally, but you are doing him and yourself a massive disservice if you don't speak to him plainly about your observations and concerns first before going to Pro Standards, ALPA, Chief Pilot, etc.
