I don't want my mother to ruin my day talking about my idiot father
I feel like you're having very bad issues at home, why don't you want your mother to talk about your father?
She won't stop talking about how much of a moron my father is and it makes me angry.
I get why you'd be upset. It's so not cool for your mom to talk about your dad badly like that.
I want to be upset about it but it's a waste of time.
It may be a waste of time, but if your family do not do something about it, then your parents may have worse problems in the future. They seem to have a marriage issue and I would urge them to go into couple's counselling so that they can try to resolve their issues and have a more positive and less  toxic living environment for you and your siblings.