'Hollback Girl' seems to be about Gwen desiring to beat the hell out of an ex-bf who is spreading nasty rumors about her.

ST*: *slaps forehead* pervert...

'all boys hit Stefani in her back' are NOT the lyrics to ANY of her songs. The closest line is sung by Eve in 'Rich Girl', when she says 'SEE STEFANI AND HER L.A.M.B.' That's the ony song that ever sings the word 'Stefani'.
...but she does say some pretty weird boy-on-Stefani stuff in 'Crash' and 'Bubble. Pop. Electric.'