On the trip to the mall, made your bitch ass plank

from 50 Cent – Love, Hate, Love Lyrics on Rap Genius

Fif is referencing a rumored altercation where The Game ran into Ice Burgandy and company at the Fox Hill Mall. They tell a story on how the beef started over twitter and how they bumped into him at the mall. It esculated and the game got knocked out. They referenced the way he laid in front of his son as planking.
http://www.youtube.com/watch?v=LfCWnjzPvXk

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