Info: how many kids do they have? What is in the other bathroom? Is it just a toilet, toilet and shower? Are their other children young enough that they need a bath? What’s your relationship with your daughter and SIL usually like? Why did your SIL not want to accept the bathroom initially? Was the bathroom in a usable state when you started or was it dilapidated? Did you push for them to accept the gift given that they had already refused? How much mess was left by the workman and could it have been a hazard to the existing children or the newborn?

I feel like there is a lot of context missing here. If you don’t usually have a strained relationship with your daughter and her husband, the fact that he’s acting so aggressive to what you see as no big deal suggests to me that either there’s an underlying issue or it’s a much bigger deal than your letting on.

Either way, I think saying you’re going to take the materials back is petty. If you want to wash your hands of the situation, thats fine. But if you have any desire to reconcile at some point, don’t go out of your way to make things worse.

I also think it would make far more sense to call your daughter or have her mother call her if things are still too fraught and ask exactly why she is upset, and very importantly, listen to the answer. Perhaps then you will no-longer be confused about why your daughter and her husband are acting as they are.