Hip hop artists (MCs, DJs, B-boys, etc) who are typically aspiring and full of themselves, yet their style is an insult to real hip hop because it (1) copies another artist's style, (2) is mainly driven by commercial aspirations, or (3) is basically incompetent with no hope of improving. Wack = weakly executed flashy moves in place of true substance.
Even the wackest rapper can be a commercial success with a major label behind him.
A person's head. Called a cabbage because of the size/shape resemblance to the vegetable. A hip hop term.
When I'm attacking wack MCs I put automatics in the back of they cabbage and blast the cortex into fragments.