It is a song about Whatsername sending a letter to Jesus of Suburbia, or St.Jimmy, and telling him how he isn't saving the city (City og the Damned). Whatsername also states in the letter that she is going to leave him and the city behind.
The lyrics of American Idiot are written in a diary form; diary of Jesus of Suburbia's. But for this song, the lyrics are written in Whatsername's writting, but not entirely.
teenie: wtf? oh that....no. whats the point? i only listen to american idiot, holiday, blvd of broken dreams and wake me up when september ends!
me: and you call yourself a green day fan?
me: you're nothing but a posuer