I bet you think this song is about you

There are many great mysteries from history. What happened to the Roanoke colony? Who was D. B. Cooper? What the hell is up with the Easter Island sculptures? But perhaps the greatest mystery is the one given to us by Carly Simon: who's so vain?

Ms. Simon has given many clues, but no solid answer as to the subject's identity, but Warren Beatty once said, "Let's be honest. That song was about me." Because irony. 

Here's a few other songs written about folks you may know.

Layla (Eric Clapton Jim Gordon, 1970)

The Layla to whom this song refers to the ancient Arabian tale of Layla and Majnun. Majnun, according to the story, was in love with Layla, but her father would not allow her to marry him, and so Majnun went insane. The Layla of the song stood for Clapton's secret love, Pattie Boyd. You might not have heard of Boyd, but you've probably heard of her then husband, Clapton's best friend George Harrison. That's pretty awkward, and it got even more awkward in 1979 when Harrison was an honored guest at Boyd and Clapton's wedding. Before the two divorced a few years later, Clapton also wrote the song Wonderful Tonight about Boyd.

How Do You Sleep vs. Silly Love Songs (John Lennon vs. Paul McCartney)
The Beatles were musical pioneers who created, among other things, the first concept album (Sgt. Pepper's Lonely Hearts Club Band), the first real music videos (they released them for Rain and Paperback Writer in 1965 instead of touring), and the first album in which all the songs were written by band members (most artists at the time performed music written by other people on their albums, and those who did have original work only had a few original songs on each album). 
After the excruciating public meltdown of The Beatles, Paul and John decided they hadn't had enough fighting and so they joined to innovate one more thing: the hip hop feud, in which they lobbed "diss tracks" at each other for the first several years of their solo careers.
John Lennon's 1971 How Do You Sleep was the most direct of these songs, with lyrics like "those freaks was right when they said you was dead" (I assume that McCartney must also have been the grammarian of the duo) and "the sound you make is muzak to my ears." 
That wasn't the catchiest song ever written, but one of McCartney's songs, 1976's Silly Love Songs (which is certainly muzak to my ears) was a response to John's complaint that all Paul wanted to write were "silly love songs."
And since I don't like either song, you get this:

Hollaback Girl (Gwen Stefani, Pharell Williams, and Chat Hugo, 2004)

This is absolutely the best song to perform on network television

This song, second only to Mickey and It's a Small World in its earworminess, is actually written about a person second only to Yoko Ono in its "talentless person only famous because of dead spouse"-iness, Courtney Love. Love, described by one of my friends as "literally the worst singer I have ever heard live" (see proof below), once said of Gwen Stefani "being famous is just like being in high school... I'm not interested in being Gwen Stefani. She's the cheerleader, and I'm out in the smoker shed." So Stefani wrote a song about being a cheerleader because... that'll show Courtney love she's not a cheerleader.

Actually, Love is kind of like the girl who drops out of high school

to form a terrible band and ends up dying in a prison knife fight.