The size of the person has nothing to do with what will trigger aggression. I'm 5'8" and ~140lbs and I can reliably bring out strong aggression in dogs I work better than 200+ and 6ft+ guys. Its all a mental game....
My first reaction is to say, he's a male dog from obviously working lines, and you got an actual GSD on your hands, congratulations... people pay good money for such a dog. The fact that he does not perceive any threat or feel the need to posture at children or women is a very good thing. Men naturally posture... at dogs to a degree, at each other pretty much non-stop, so it could be an appropriate response to the man.
Please take some video of this happening. I can then tell you better what I think might be happening and what you can do to "fix it" and if it can be "fixed". I need to see both the dog, and the person approaching.
Hunter, CWDC UScA Helper
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