It is rude to not help your parents.
Dave is at home when his father calls and asks Dave if he would mind coming over to help him clean the garage.
Dave wants to answer his father's question.
Dave tells his father that he would be glad to help him and that he'll be right over.
Dave tells his father that he is really busy the rest of the day, and he just can't put anything off right now, so he can't come.
Dave's father is delighted that he will get some help and that he has such a good son.
Dave's father is disappointed that he can't get help from his son and a little stressed about his workload.