How you sold grams? You ain't never served a brick
It's like you got no hands -- you ain't got a bird to flip

from J.R. Writer – Intro Lyrics on Rap Genius

Writer doubts his antagonist’s drug dealing bona fides. A “brick” is a kilo of cocaine. The pun here is that “bird to flip” both means “kilo of cocaine to sell” and “middle finger to throw up” — thus the “no hands” line

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