hollaback girl
hollaback girl - A girl who fights back with her mouth in response to a dude who picked a fight in the first place with the dude's own mouth. A verbal fight of sorts.

Ain't no hollaback girl - a girl who ends fights with her fists in response to a dude who picked a fight in the first place with the dude's own mouth.
My next-door neighbor is a loud mouth, but I ain't no hollaback girl. 

In Hollaback Girl, Gwen fights back against a shit-talking dude. She's not responded before to verbal attacks, "been around that track," but not anymore - "so it's not just gonna happen like that." Now she's fighting back.

"Put your pom poms down" - close your open mouth.

I think Gwen also means "shit" both figuratively and literally - the dude is bananas, crazy, for talking shit, but, well, bananas are shaped like what? 

This shit is bananas
B-A-N-A-N-A-S

The chorus and repetition and drums are like a war song chant, with the warrior girls in the car and the troops on the ground heading to the battleground to deal with the shit-talking dude. I kept waiting to see the dude at the end of the music video, and was disappointed he/she didn't turn up. Anyhow I think that the dude probably lives next door to me.