My father need's a good smack!!! 😠

My 8 year old sister went over and sat on dad's lap just a moment ago and he says to her "what are we gonna do about that shirt you're wearing? Because it's wrong". The shirt says " Strong like mom". Like how dare he? I don't care how much he hates my ex step mother, you DO NOT talk badly about your daughters mother in front of her! It is not ok! Keep your mouth shut and horrible words to yourself! I get so suck of him saying thing's like that. I would rip him a new one, but I don't want to do that in front of my sister. My father was also recently diagnosed with a small form of autism, so he may not even realize what he is saying is so terrible, but still.