OK. Here's what Gwen was thinking when she made up that word:
Hmmmm.... What can I put in my song that will drive everybody insane trying to figure out what it means? ....Hmmmm.... I know! How about hallaback girl? That will drive them bananas! Hey! i could put that in the song too!
Uggh. There is no such thing as a hollaback girl. Was Gwen on crack?