Seeing as the first line of the song mentions "coastline", I think PCH stands for Pacific Coast Highway. Let's look at additional lyrics in PCH that would support this theory: "surf's up", "Eatin' up asphalt", "By the deep blue sea", "Want to head north, but I might go South" (as the Pacific Coast Highway is made of asphalt, is by the Pacific Ocean, and runs North and South.
Nice try... PCH has about as much to do with the ocean as their song "pearl necklace"... The pearl necklace isn't made of pearls and PCH isn't a highway. PCH is Post Cum Head. (almost all their songs have sexual references.) It's A true blood blue slut not sud. Anyone know who Brian is? That's my question...