holla back
correctly spelled 'Hollaback', a word made up by Christina Aguilera that subsequnetly has no uniform definition.

I suppose it is said to gain attention, or do something once more. It might also mean 'scream backward', which makes little sense in and of itself.
Person #1: I Listen to the song Holla Back girl yesterday, I think my ears are still bleeding.
Person #2: Why can't Christina Aguilera die already?