Mick Jagger actually sings backup on You’re So Vain, so I’d be awfully surprised if the song really was about him. I doubt Mick’s sense of humor is good enough to perform on a song that makes fun of him.
Excuse me… does this rhyme?
The backup vocal does sound exactly like Mick Jagger, and as Kyla notes, its not likely to be about him for that reason. Carly Simon did apparently date Warren Beatty, and the song does fit him perfectly, or at least it did in his narcissistic under 50 years old days.
However, I always like to tell people that, yes, I do think it is about me.
Perhaps the song isn’t about any one specific person, but about a type of person, several of which Ms. Simon has known. Being in the rock music biz, she likely knows many men like this. Thus, any one man who hears it and thinks it is about him is being overly vain about his importance.
While we’re at it, what the hell are “clouds in my coffee?” The phrase just pisses me off. Damn Carly Simon and her indecipherable lyrics. Damn her to hell.
[waxing nostalgic about my brief career as a stripper] Breezy always claimed exclusive rights to dance to “You’re So Vain”. None of the other girls dared to use it in their sets. I think it was my second or third night at Knocker’s (yes that really was the name of the joint) I innocently fired up that song when I was programming the jukebox for my set, and Breezy about stormed the stage, screaming, “This is my song. This is my song”.
Breezy was so vain, she probably thought the song was about her.[/waxing nostalgic about my brief career as a stripper].
FWIW, on the Janet Jackson version of the song Carly says,
“The apricot scarf was worn by Nick, nothing in the words refer to Mick”
Though Janet’s version is definitely about her ex. I think.
I thought the whole point is, she’s deliberately being coy. And anyone who thinks the song is about him is fulfilling that-if you think this song is about YOU, that proves it. It could be anyone-but for you to think yourself so important…
Plus, it’s kind of catchy!
Hehe and I thought this was a Nine Inch Nails thread…
“Youre so vain, I bet you think this song is about you, dont you? Don’t you? Don’t you? Don’t you?” (Starfuckers Inc.)
“I had some dreams, but they were clouds in my coffee, clouds in my coffee…”
To me, she is making a comparison of her shattered dreams to the moment when you pour cream into your coffee and “clouds” appear but quickly disapate when you stir the coffee to blend it all together. Her dreams were temporary and disappeared too quickly. YMMV.
Of course, you may have just been making a joke. Please dont “whoosh” me. 
btw, did she even write the song?
A friend once told me he’d thought she was singing “clowns in my coffee.” And now I can’t hear that lyric without giggling.
You’re so vain,
'Cause in the desert, there ain’t no one for to give you no pain.
Yes, Carly Simon wrote “You’re So Vain”.
BTW, Sparticus, the above link also specifically credits Mick Jagger with backing vocals. It actually is him on “You’re So Vain”.
I’ve always held to the belief that she wrote the song when she was breaking up with James Taylor (I’m sure I heard that somewhere about 25 years ago) but I guess I’m wrong.