Why is the woman angry with her son?

M: You look furious, Mary. How come?
W: My son had an accident. He wasn’ t hurt, but my car was damaged.
M: But it wasn’ t too bad.
W: Sure. But he is still taking driving lessons. He just ignored my warning.
M: He should have known better.

W: Do you know this is the first time we have been all together for dad’ s birthday since his retirement?
M: Yes, I do. I am sorry about that. I was working.
W: All right. We saved you a piece of cake in the fridge.