It is a such huge buildup to the big day. And it's so challenging if you have a DC that hasn't learned how to express clearly what they do want. I learned the hard way to manage expectations.
We decided that our kids can ask Santa for three things, max. And of those three things, Santa may choose one or two. And might leave some surprises in their stockings. Otherwise, our DCs really will expect the whole Smyths toy catalogue.
Even then, Santa can't fit everything they ask for in his sleigh. Santa could not fit a hoverboard in his sleigh this year; the child who wanted this was told straight away, as soon as she expressed that wish. Santa doesn't deliver iPads or consoles or pets to our house either.
Santa may know your heart's desire, but the Elves are a bit thick, and it's the Elves who make the toys. They need some help figuring out what you want.
Our oldest is the child who has the hardest time expressing what she wants. Some of that difficulty is probably rooted in people-pleasing (not wanting to express the "wrong" thing). She's a teenager now, but when she was smaller, she genuinely used to expect us all to read her mind.
That's gotten better with time, but it took some effort on my and DH's part to draw it out of her. How to Talk So Kids Will Listen and Listen So Kids Will Talk had a lot of good advice for us.
I understand feeling easily frustrated with one of your children. I go through that with each of mine sometimes. Usually easier to get past if we find a way to spend time together that's fun for both of us. Eg, I don't enjoy playing pretend with my youngest for that long because she gets really bossy and complains when I try to do anything. But we have a much nicer time together when we're on a hike through the woods, building fairy houses, playing in the park, baking, or if I'm reading to her.
If you can find the thing that you and your DS both enjoy doing at the same time, you might be able to do it together and strengthen your bond that way. Besides giving him more security in his relationship with you, it might give you more security too? Just a thought. Sorry you've had an upset morning already. and hope it gets better. 