Parents (and people in general) tend to argue a lot. It can even become routine for families who have a drinking father:
He drinks after work. He gets drunk and angry. He begins to yell at the mother about stupid things. She tries to defend herself. It's a lot of yelling. Children become scared. Everyone falls asleep eventually feeling bitter or afraid. They wake up the next morning and hardly ever bring up the night before. Apologies may or may not be said. Everyone tries to be extra nice to each other. The night before feels like just a bad dream. Yet it happens again that night. It's a never-ending pattern.
The Wall's family is also experiencing this. The author recounts one time when they were driving and her mother was pregnant at the time. She announced that she believed the baby would be coming soon and Rex and her disagreed about how long she had been pregnant. He had been drinking and accused her of messing up in her counting. The author quoted her parents' argument and her mother eventually slammed her foot on her husband's which was resting on the brake pedal. The car screeched to a stop and the mother leaped out of the car and ran into the darkness. Rex chased her and cussed at her, telling her to get back in the car. Eventually he cornered her and drug her back into the car as she cried and screamed.
The author says her parents make up the next morning. Everyone seems to be in a good mood and when her mother cuts her father's hair he exclaims that she did an amazing job. I doubt a word was mentioned about the night before. Drunks usually don't remember what they did so they don't apologize.