36 O's so riding round with that nina
He has drugs in his car, so he has to keep a gun with him.
Nina = Nine millimeter gun.
36 O’s = 36 ounces = 1 kilo of whatever drug he has on him, most likely marijuana since it is the only drug commodity for which it is customary to measure in imperial units (cocaine and other class A drugs are generally measured in grams or kilos).
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