Incompetent ain't the half of it
Incompetent: not having or showing the necessary skills to do something successfully, hence why he follows incompetent up with ‘'ain’t the half of it’'
So, Slight wordplay while describing his so called ‘'homies’‘ as incompetent.
To help improve the meaning of these lyrics, visit “V. 3005” by Childish Gambino Lyrics and leave a comment on the lyrics box