RACHEL: We were supposed to meet for lunch, but he didn’t show.
First Luke leaves the diner just as it opens, and now he’s skipping coming home for lunch with Rachel in order to do work on Lorelai’s house. No wonder Rachel is suspicious and resentful, and seems hurt and upset. Notice that this is a slight echo of Madeline being “out to lunch” – by skipping lunch, it shows Luke is losing contact with his life with Rachel.
Notice that in the background the Stars Hollow Fire Department is holding a fundraiser – a sign that problems have reached emergency levels in Rachel and Luke’s relationship. Lorelai is wearing red to match the fire engines, showing the source of the emergency.