Why was Jonathon's mother such a biotch?
When she corrected Grace on her grammar?
What was the point of that?
The point of the scene was to establish that Jonathon was a bit wrong in the head, what was added by portraying the mother as a pedantic dick?
If it was meant to illicit some sympathy for Jonathon from the viewer, it didn't work at all given the context of the rest of the conversation.