The text is an anthem against bullying, in fact, as Taylor Swift explained, it talks about criticism: not constructive criticism, not professional criticism, but the kind done when one is simply being mean.
Inspired by a deeply personal experience of Taylor Swift, it's a song that many can relate to, as well as a venting against all those people who, just out of meanness, say things that ruin our days, as Taylor Swift said. Moreover, it is also a message of hope, because the song also speaks of the revenge that Taylor Swift is taking on these people, having become a successful singer, while they have remained nothing more than mean people.
The song has an ironic and irreverent tone, yet is tinged with bitterness, and these characteristics make it a truly liberating, engaging, and at the same time retro and elegant anthem, which is not surprising since it is one of the most Country tracks on "Speak Now".