Haters gotta go on iTunes to go get me
This implies that the haters have only heard his albums, and not his free mixtapes (which are not available on iTunes), which are a better display of his rapping abilities
This also means people have to go on iTunes(buy his music) to hear it and then hate. OR
They gotta come up with their own song on iTunes, in order to take a shot at him.
To help improve the meaning of these lyrics, visit "Watch My Shoes" by Lil Wayne Lyrics and leave a comment on the lyrics box