Don't trifle with the emotions of singer-songwriters. As this list will prove, they like wreaking vengeance through song. Many people -- like, anybody with ears -- assumed that Justin Timberlake's Grammy-winning 2004 hit "Cry Me a River" was directed at ex-girlfriend Britney Spears. (The video even featured a Britney look-alike in the role of the woman whose home Timberlake breaks into.) Paired with his later hit "What Goes Around Comes Around," the song offers a handy life tip: Be nice to Justin Timberlake.