First she makes the "Oh" face then she give me pea brain

from XV – Warmup Freestyle Lyrics on Rap Genius

Meaning

Two consecutive letters used. O Face and P brain. Nice one Vizzy.

Playing on those letters she’s most likely going to perform oral on him. He is going to give her his penis. Pea Brain (head of his dick)
Also a reference to the “Oh Face” scene in Office Space
http://www.youtube.com/watch?v=QzIN3EgBIHg

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