Flexing, they know flexing (beep, beep, beep)
Niggas know I'm flexing, they know I'm flexing

from Chief Keef – Finessin' Lyrics on Rap Genius

Meaning

Here, Chief is stating he’s flexing/flashing his newly attained riches on his haters.

Subsequent to stating this, “beep beep beep” refers to the amount of money that is coming out of an ATM.

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