So so true unsolvedmystery.
Unfortunately, a lot of the time, we don't realise how our communication is affected by how we feel about someone. My DS has hit the dreadful teenage stage which makes him...well not the most lovable person except by his mum because someone has to! I deal with it the way we parents tend to, by picking our battles. OH, who is a wonderful loving person has been finding much harder to cope with the behaviour. I understand this because when you don't have that parental blind love that makes you cope with the worse because when things are good, they are usually aimed specifically at those parents who they really do love back, you don't have that same balance.
As a result, my OH has detached himself from DS. Probably the best thing he could do in many ways as he feels less frustrated this way and DS less targeted. However, the one thing that OH doesn't see at all, but I and I'm sure DS do is that the tone of voice my OH takes with him very much reflects how he feels about him. It's little things, like if I leave the door open, he'll say 'darling, do you mind closing the door', whilst if it is my DS he might say something like 'do I have to say it again, please close the door'. Or DD will come home and he will ask her how her day went, but won't ask DS. Or even saying goodnight, which might be 'goodnight C, sleep tight' looking at her in the eye and a smile, whilst it will be a rushed 'nightnight' without looking up at DS.
Thankfully, I was able to talk to him about it, he listen and even though at first he said he didn't speak to him differently, I think he reflected on it and had to admit that he did use a different tone of voice that was reflective of his feelings. It was a vicious circle, because of it, DS didn't engage with him at all which of course made OH feel less engaged with DS. OH made a real effort with his communication with DS, I really noticed it and unsurprisingly (to me) it had a real positive impact on DS who started to take the initiative to talk to OH. As a result, their relationship has vastly improved in the last few months.
I do expect things will remain tense for a few more years. We went through exactly the same with DD when she was 12 and OH find it really hard to relate to her, but three years on, they now get along brilliantly.
I really do believe that when things are not good between adults and children, let it be parents, step-parents, teachers etc..., the onus is on the adult to make the first efforts to improve communication, not the child. Children react to what they feel as UM as said. It can take time so it can be quite disheartning but a child who doesn't have social issues as a whole but is rude to a SP is often a child who doesn't feel appreciated themselves for whatever reasons, and it is these reasons that need to be explored, whether they are funded or not.