This song is about a guy who gets dumped by his very attractive girlfriend because she is looking for a rich man to take care of her (the "sucker in the three-piece suit"). This sugar daddy is fat and bald, but he's got the cash she's after.
The line "Nine on a 10 scale" is a reference to the 1976 solo album of that name by lead singer Sammy Hagar.
"Sloop John B" is a traditional West Indian folk song, and it was a huge hit for The Beach Boys in 1966. They tweaked the lyric, "This is the worst trip since I've been born" to "...I've ever been on" as a wink to acid culture.