Is this disrespectful ?

We were all over at my mothers house as a family swimming in the back yard. My mother was talking to me, my (13 year old)step son, and my hubby about putting some oil in his very curly and matted hair( his father will not make him take care of it. I have tried everything in my power to get either of them to take care of it, my mother and I are both hair dressers.) Step son immediately gets mad and says “okay I’m out of here. “ my mom turns and says “where are you going?” Step son “Umm in the house to get a snack where else?”. My mother looks shocked and he goes in the house. I immediately looks at my mother and then my husband he says “what?” I said “he’s fucking mouthy.” My husband blank stares at me and says nothing and never correct step sons behavior I finally brought it up tonight that I was still upset about him letting my step son talk to my mother like that. And my husbands claims it is not disrespectful in his eyes and completely acceptable. I told him if he did not correct the behavior that next time I will because my kids are not allowed to treat my mother that way so neither will my step son. His response is I’m crazy and irrational…. So my question is this disrespectful?