The problem is really that so often we do not let people know that they have been rude.
I know someone who is often rude (not just to me)
I pull him up about 1 out of 6 times. Every time he reacts strongly. One thing he says is that this is 'just him' and people who know him well understand he isn't trying to be rude. Well I've knowm him for several years, and no, that is not an excuse, sometimes he really crosses the line.
I hold my ground, and finally he goes away and thinks about it and usually then apologises (I suspect after he has sounded off to his wife and she has told him he is unreasonable)
Everything is fine for a few months and then he does it again.
To be honest, I don't care, and would let it go, but he does it on a group whatsapp, and I know others are upset, but not brave enought o say anything.
We need to address rude behaviour properly, calmly and more often.
So when your friend messes you around, you need to say - you keep messing me around with arrangements and this is actually a pain, and it is pissing me off. I understand that plans change, but can we make a realistic plan, and then stick to it please.