Finally standing up to him.. Need some encouragement

[IWantAMooseCalledDominic]

Could do with some objective opinions. Have lurked on this board for years but never posted before.
My ex dropped our 5 year old son back to me this evening without his jacket (which he obviously needs for school tomorrow). He laughed it off when I said ds needed it for the morning saying I could put extra jumpers on him. I replied that it's too cold to do that and I've no other coats here that fit him properly, and could he drop it back down. He then got angry with me saying I can't adapt and he knows I've other coats then walked back to his car shouting that he wasn't going to bring it down and it was my fault he forgot it because I was rushing him (I'd rang him 40 minutes prior to this to find out was he on his way back with ds as it was getting late)

Despite having left him nearly 3 years ago, I'm only now starting to properly stand up to him, and I want to send him a message telling him I won't tolerate him speaking to me like that at my home and in front of our son, but part of me is still so scared of standing up to him and making the situation worse.
Please help me to not be so spineless

[Cricrichan]

What an idiot! I would only send a short message asking him to bring his coat as he has no adequate alternatives. Don't engage in conversation with him or arguments. If he rants or is disrespectful then walk away and shut the door etc.

[PickAChew]

Tell him to fuck the point scoring - it's your DS who will be cold.

[Wolfiefan]

He can either bring the coat to you or drop it at school tomorrow am. First thing!
Do you have a formalised contact agreement?

[IWantAMooseCalledDominic]

No, nothing formalised. Have text asking, well begging, him to bring the coat in the morning though I'm not holding out too much hope. He's so unbelievably selfish.