We adapt to crime
Pack a van with four guns at a time, with the sliding door, fuck is up?

from Kendrick Lamar (Ft. MC Eiht) – M.A.A.d City Lyrics on Rap Genius

Meaning

They’re so used to crime that they have adapted to that lifestyle. Now they don’t go anywhere without a few guns on them.

Also, the van with the sliding door is a returning motif throughout the whole album. Sliding doors make it easy for gangbangers to perform a drive-by. It is probably Kendrick’s parents' car which is even on the cover of the deluxe version of the CD.

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