How do you deal with people not respecting your wishes?

My father in law has kissed my newborn repeatedly despite me saying this is absolutely not ok. I don’t even kiss him.

It s even if more frustrating because we are having to stay with them for the week due to some urgent work being done at our house (far too dusty for baby to be around)

What would you do? Do I just need to snap even more? Or refuse him to hold him? I don’t want to seem dramatic but baby has already been to hospital with an infection and he’s only 3 weeks!