Personal space is cultural phenomenon that at times gives me trouble. In USA that 3-4 feet is appropriate, in many cultures it is much less, in mine it is more. Always having trouble with it when living my own country. But of course when someone whose concept of appropriate personal space is different it is not about boundary violation but just different set of boundaries. I just had issues with that with a difficult child's friend, Californian guy who ended up living with us for couple of weeks last fall and after that visiting us at least once a week or more. Really nice young man, but darn did he come close and was loud. He had hard time adapting to more personal space needed in our culture compared to USA. Even after we explicitly explained it to him (when he didn't seem to take a hint that everyone was always taking a step back when he came to talk), he often forgot. He was not malicious in anyway so it was only slightly uncomfortable.
But breaking that personal space boundary (even in very slight way) can be used to intimidate or to show dominance and that is something I have needed to fight against in my family. Not so much with difficult child, when he was young and could hit me in rage, he did that, but other than that already then but even more so later, he in fact takes more space when he is upset or angry. He fights with hurling insults or sneaky, passive aggressive ways and doesn't get to your face physically (I mean, he does go to other side of the room to hurl all the nasty things that come to his mind, if he can. And afterwards he may go and slice your car tyres (you don't believe how many sets of tyres I have needed to have repaired or bought new ones because of that habit of his), break or hide or steal something valuable of yours, go and spit to the jar of sour milk only you drink or something like that, but he is not into your face type of fighter. My husband, and in some degree my easy child, are.
It took me years to teach my husband that I really didn't like or accept him trying to dominate me physically. He is a big guy and has always been. Oldest child in his family, tall to his age from the get go. He did learn to intimidate others with his size. While he isn't violent per se, he uses his size to give you a threat. He isn't into your face literally, it is much more subtle. Maybe just half a feet too close, leaning towards you, hands not in fists but very assertive body language, bit louder voice than necessary and so on. It is so subtle and most people have great difficulties defining it aggressive (which is why it works for him, open aggressiveness would be a big no no in his surroundings.) I had to tell him again and again, that he needs to take a step back, that I was not arguing with him, when he tried to intimidate me and if he wanted to talk with me, he needed to give me my space. He did finally learn, but unfortunately only with me. He still uses those same tactics for example with our sons. And difficult child can get really anxious because of that and is not able to keep his own and calmly tell him to take a step back. Till now difficult child has caved, but I have to say that there have been times, when I have been really afraid, that this would be the time that difficult child doesn't back away, but actually attacks back. It would be catastrophic. Not only mentally to both of them, but as I said, husband is a big and strong guy, difficult child is even bigger and pro athlete. It would be ugly.
I have talked with husband about it. Pointed out that all the men in difficult child's life who can efficiently communicate to him even when he is upset use the opposite tactics. Back away, give difficult child some space, sit down, speak with lower voice instead of louder when difficult child is upset and so on. At times husband remembers, but when he is also upset, he tends to slide to these old habits.
Unfortunately easy child has copied husband's behaviour in this. He doesn't do it to me, I squashed the first attempts when he was still young and that has stuck. But I see him doing it to his friends and also difficult child at times, when he thinks I'm not seeing it.
Both husband and easy child are very socially aware and are so subtle with it, that they really get away with it most of the time. I find it very ugly habit, if you ask me, but then again, I'm like difficult child and need more personal space when upset, not less.