I suspect it was a composite of a few individuals. Kristofferson, Jagger, and Warren Beatty all seem to fit the song perfectly, so I'd bet there's a little piece of all of them in there. I'm gonna go out on a limb here and give Warren the biggest piece. LOL!

To compare Carly Simon to Brittney Spears, however, is kind of like comparing a magnificently painted oil portrait by one of the masters to one of those black velvet paintings of Elvis you see in the dollar store. ;-)