CHRISTOPHER: [sighs] Why does your dad have more faith in me than you?
LORELAI: My father hit his head surfing Rincon a couple of years ago. His judgement’s a little off.
Rincon Beach is a surf spot in California, between Malibu and Santa Barbara, and closer to the latter. It’s one of the most famous surf beaches in California, and is well known around the world. It hosts the Rincon Classic surf event each January, and is mentioned in The Beach Boys’ song Surfing Safari.
Obviously Lorelai is joking – surfing Rincon is one of the last things Richard Gilmore would ever do. The real reason for his misplaced faith in Christopher is explained later in the episode.