Hilarious antics were not what forced Brian's parents to confront the nitwits who waited at home for them. They allowed themselves to be instead taken hostage, if the fools agreed to not kill each other. They told Brian to wait at the Bannisters' for them.
"What if you don't return?" said Brian.
"Then I guess your Aunt Fern can take you in," said Brian's father.
"Yes," said Brian's mother. "Pray we return."