Excuse the mess it made, it usually doesn't rain
In Southern California,
Alternatively it could be a reference to the Albert Hammond song: It Never Rains In Southern California, the song concerns the struggles of a singer who moves out to California to pursue a career in Hollywood but does not have any success and deteriorates in the process.
California is a happy place. A place where it doesn’t rain.
When Frank tells his guest to excuse the mess, he is just talking abut how he’s messed up in the head. Whether from Katrina or some other life experience or relationship.
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