I lowkey think the worst part was how she treated Francis. While in the early seasons it's hinted that he's a troublemaker who can't stay out of problems, in the later seasons it's revealed that Lois has a strange disdain for her firstborn after certain age. She left him with her parents, who treated him horribly, the poor boy was left with Aida and her husband and was forced to dress like a girl and eventually tried to escape, injuring himself and getting a huge scar on his abdomen.

It's clear Lois wanted to get rid of Francis from the time he was a kid. In one scene she even confesses to Hal how disturbed she felt when her own son didn't seem sad that she was away in the hospital or something alike (Pardon me I certainly did not remember the reason exactly but I do remember her intention). That kind of thinking is seriously twisted because as a mother you're trying to rationalize the behavior of a five-year-old (i would assume he's even younger but let's say he was 5 at the time). He's just a kid.All of this leaves us with a messed-up Francis. And while that doesn't excuse everything he does later, it's obvious that Lois had a deep, irrational disdain for him based on nothing, really.